U.S. patent application number 14/237715 was filed with the patent office on 2015-12-03 for viscoelastic silicon rubber compositions.
This patent application is currently assigned to UNIVERSITY OF VIRGINIA PATENT FOUNDATION. The applicant listed for this patent is Louis A. Bloomfield. Invention is credited to Louis A. Bloomfield.
Application Number | 20150344635 14/237715 |
Document ID | / |
Family ID | 47669003 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150344635 |
Kind Code |
A9 |
Bloomfield; Louis A. |
December 3, 2015 |
VISCOELASTIC SILICON RUBBER COMPOSITIONS
Abstract
The invention provides for new viscoelastic silicone rubbers and
compositions and methods for making and using them. The invention
provides for viscoelastic silicone rubbers that are stiffer on
short timescales than they are on long timescales. When subjected
to brief stresses, they are relatively stiff and elastic, and they
resist changing shapes. When subjected to sustain stresses,
however, they are relatively soft and accommodating, and they
gradually change shapes. When those stresses are removed, they
gradually return to their original shapes. These viscoelastic
silicone rubbers resist compression set and they are extremely
resilient in response to sudden impacts. They can be dense rubbers,
foam rubbers, and particles.
Inventors: |
Bloomfield; Louis A.;
(Charlottesville, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bloomfield; Louis A. |
Charlottesville |
VA |
US |
|
|
Assignee: |
UNIVERSITY OF VIRGINIA PATENT
FOUNDATION
Charlottesville
VA
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150045471 A1 |
February 12, 2015 |
|
|
Family ID: |
47669003 |
Appl. No.: |
14/237715 |
Filed: |
August 10, 2012 |
PCT Filed: |
August 10, 2012 |
PCT NO: |
PCT/US2012/050419 PCKC 00 |
371 Date: |
October 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61521799 |
Aug 10, 2011 |
|
|
|
61532167 |
Sep 8, 2011 |
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Current U.S.
Class: |
521/154 ;
524/588; 525/479 |
Current CPC
Class: |
C08G 77/20 20130101;
C08G 77/38 20130101; C08K 2003/387 20130101; C08L 83/04 20130101;
C08K 3/38 20130101; C08G 77/16 20130101; C08K 5/5425 20130101; C08K
5/55 20130101 |
International
Class: |
C08G 77/38 20060101
C08G077/38; C08L 83/04 20060101 C08L083/04 |
Claims
1. A viscoelastic silicone rubber composition comprising: (a) at
least one polyorganosiloxane comprising at least one
ethylenically-unsaturated group; (b) optionally at least one
permanent crosslinking agent; and (c) at least one temporary
crosslinking agent; wherein the composition contains sufficient
permanent crosslinks to give the composition an equilibrium shape
and sufficient temporary crosslinks to give the composition a
stiffness that is greater on short timescales than it is on long
timescales.
2. A viscoelastic silicone rubber composition comprising: (a) at
least one branched polyorganosiloxane; (b) at least one permanent
crosslinking agent present in an amount to provide sufficient
permanent crosslinks to give the composition an equilibrium shape;
and (c) at least one temporary crosslinking agent present in an
amount to provide sufficient temporary crosslinks to give the
composition a stiffness that is greater on short timescales than it
is on long timescales.
3. A viscoelastic silicone rubber composition comprising: (a) at
least one polyorganosiloxane; (b) at least one permanent
crosslinking agent present in an amount to provide sufficient
permanent crosslinks to give the composition an equilibrium shape;
(c) at least one temporary crosslinking agent present in an amount
to provide sufficient temporary crosslinks to give the composition
a stiffness that is greater on short timescales than it is on long
timescales; and (d) at least one softening agent present in an
amount sufficient to make the average lifetime of the temporary
crosslink of shorter duration than the average lifetime of the
temporary crosslink in the absence of the softening agent.
4. A viscoelastic silicone rubber composition of claim 1, wherein:
(a) the polyorganosiloxane comprising at least one
ethylenically-unsaturated group is prepared from a
silanol-terminated polyorganosiloxane polymers of formula (I)
##STR00006## having a molecular weight ranging from 400 to 50,000
Dalton and a viscosity ranging from 10 to 10,000 cSt and preferably
from about 15 to 2,000 cSt and wherein "m" is 1 or greater and
represents the number of the repeating units in parentheses to give
the molecular weight of the particular polymer; (b) the permanent
crosslinking agent is selected from a vinyltriacetoxysilane,
vinyltrimethoxysilane, vinyltrichlorosilane, and
vinyltriethoxysilane; and (c) the temporary crosslinking agent is
selected from a boron-containing compound, a titanium-containing
compound, an aluminum-containing compound, or a mixture
thereof.
5. (canceled)
6. (canceled)
7. The viscoelastic silicone rubber composition of claim 1, wherein
the polyorganosiloxane is silanol-terminated.
8. The viscoelastic silicone rubber composition of claim 1, further
comprising at least one linear polyorganosiloxane.
9. The viscoelastic silicone rubber composition of claim 1. wherein
the polyorganosiloxane is partially crosslinked and has at least
three terminal silanols.
10. The viscoelastic silicone rubber composition of claim 1,
wherein the polyorganosiloxane is branched.
11. (canceled)
12. The viscoelastic silicone rubber composition of claim 1,
wherein the permanent crosslinking agent is a siloxane bond-forming
crosslinking agent, a carbon-carbon bond-forming crosslinking
agent, or a mixture thereof.
13. The viscoelastic silicone rubber composition of claim 1,
wherein the permanent crosslinks are formed using condensation-cure
crosslinking, addition-cure crosslinking, peroxide cure
crosslinking, or a mixture thereof.
14. The viscoelastic silicone rubber composition of claim 1,
wherein the permanent crosslinking agent is present in amount
ranging from about 0.02 wt % to 10.0 wt %.
15. A viscoelastic silicone rubber composition of claim 1, wherein
the temporary crosslinking agent is selected from a
boron-containing compound.
16. A viscoelastic silicone rubber composition of claim 15, wherein
the boron-containing compound is selected from boric acid,
trimethyl borate, triethyl borate, and tri-isopropyl borate.
17. A viscoelastic silicone rubber composition of claim 1, wherein
the temporary crosslinking agent is present in amount ranging from
about 0.01 wt % to 20.0 wt %.
18. A viscoelastic silicone rubber composition of claim 1, further
comprising at least one softening agent.
19. (canceled)
20. (canceled)
21. A viscoelastic silicone rubber composition of claim 18, wherein
the softening agent is present in an amount sufficient to make the
average lifetime of the temporary crosslink of shorter duration
than the average lifetime of the temporary crosslink in the absence
of the softening agent.
22. A viscoelastic silicone rubber composition of claim 18, wherein
the softening agent is present in an amount ranging from about 0.01
wt % to 5.0 wt %.
23. A viscoelastic silicone rubber composition of claim 1, further
comprising at least one filler.
24. (canceled)
25. A viscoelastic silicone rubber composition of claim 1, further
comprising optionally at least one additive, and/or at least one
catalyst, and/or at least one blowing agent, and/or at least one
passivating agent.
26. (canceled)
27. (Canceled)
28. (canceled)
29. (canceled)
30. (canceled)
31. (canceled)
32. (canceled)
33. A method of making a viscoelastic silicone rubber composition
of claim 1, comprising the steps of: reacting a polyorganosiloxane
with a temporary crosslinking agent or group under conditions to
produce a temporary-crosslinked-containing polyorganosiloxane,
adding a permanent crosslinking agent or group, a catalyst, an
optional filler, and an optional foaming agent to the
temporary-crosslinked-containing polyorganosiloxane to form a
mixture; and curing the mixture under conditions sufficient to form
a viscoelastic silicone rubber composition.
34. (canceled)
35. (canceled)
36. (canceled)
37. (canceled)
38. (canceled)
39. (canceled)
40. (canceled)
41. A shaped article comprising a cured viscoelastic silicone
rubber composition comprising the reaction product of a
viscoelastic rubber composition of claim 1.
42. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application No.
61/521,799, filed Aug. 10, 2011, and 61/532,167, filed Sep. 8,
2011, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Soon after Rochow invented polyorganosiloxanes or
"silicones" (U.S. Pat. Nos. 2,258,218-2,258,222), McGregor
discovered that heating boric acid together with silicones produced
a viscoelastic fluid that became known as "bouncing putty" (U.S.
Pat. No. 2,431,878). This remarkable fluid rebounds almost
perfectly when dropped on a hard surface yet, like any fluid, it
has no fixed shape. More specifically, bouncing putty responds
elastically to sudden impacts, but flows slowly in response to
prolonged stresses. Bouncing putty has a viscosity that increases
with rate of shear, so it is a shear-thickening fluid or,
equivalently, a dilatant fluid.
[0003] Since its discovery, bouncing putty has been improved and
modified in a number of ways. Wright (U.S. Pat. No. 2,541,851)
added a filler such as zinc hydroxide to the putty to improve its
bounce. Martin (U.S. Pat. No. 2,644,805) showed that bouncing putty
can be formed from boric acid and tetramethyl disiloxane diol-1,3.
Boot (U.S. Pat. No. 3,177,176) found that adding silica reinforcing
filler to the silicones before adding the boron compounds caused
the bouncing putty to form more quickly and at a lower temperature
during the subsequent heating step. Boot (U.S. Pat. No. 3,213,048)
discovered that bouncing putty can be formed at room temperature by
adding alkyl borates to silanol-terminated polydimethylsiloxanes
(PDMS).
[0004] Beers (U.S. Pat. No. 3,350,344) found that adding an
ammonium carbonate salt to bouncing putty prevents the putty from
flowing under the stress of its own weight and from staining
fabrics. Dean (U.S. Pat. No. 3,661,790) prepared glowing bouncing
putty by adding activated zinc sulfide and also reduced the putty's
density by incorporating small transparent spheres. Kaiser (U.S.
Pat. No. 3,677,997) added polyglycols to bouncing putty and thereby
reduced its tendency to become tacky upon extended kneading or use.
Mastrangelo (U.S. Pat. No. 4,054,714) discloses that adding noble
metal particles to bouncing putty renders that putty electrically
conducting. Minuto (U.S. Pat. No. 4,371,493) discloses a method for
producing bouncing putty from a dimethyl silicone gum, a boron
compound, and a reinforcing filler. Christy (U.S. Pat. No.
5,319,021) added discrete elastic particles to bouncing putty to
obtain a material that largely recovers its initial form when a
deforming stress is removed. Christy (U.S. Pat. No. 5,607,993)
subsequently added thermoplastic microspheres to bouncing putty to
reduce its average density to approximately 0.6 g/cc.
[0005] Bouncing putty is not, however, the only example of boron
being added to silicones. Rochow (U.S. Pat. No. 2,371,068) employed
boric acid esters as dehydrating agents for silicols. Nicodemus
(U.S. Pat. No. 2,442,613) added boric acid or an organic borate to
a heat-hardenable silicone to prevent copper from corroding when
the silicone is vulcanized onto that copper. McGregor (U.S. Pat.
No. 2,459,387) employed boron trifluoride as a dehydrating agent.
Upson (U.S. Pat. No. 2,517,945) combined a silanediol with a
boronic acid to obtain a thermoplastic copolymer, but noted no
unusual viscoelastic properties in the finished copolymer. Dickmann
(U.S. Pat. No. 2,721,857) found that adding 0.005 to 0.090 wt %
boron compound to unvulcanized silicone elastomer stock improved
the handling of that stock and reduced its stickiness, but teaches
that "when the boron compound is present in an amount exceeding the
upper limit set forth above [0.090 wt %], the physical properties
of the resulting silicone elastomer are seriously impaired."
[0006] Nitzsche (U.S. Pat. No. 2,842,521) found that boric acid
hydroxyl complexes act as catalysts for the curing of
organosiloxane resins, but noted no unusual viscoelastic properties
in the finished polymer. Brown (U.S. Pat. No. 2,983,697) added 0.01
to 0.16 wt % boron as tris-triorganosilyl-borates to silicone
elastomers to retard crepe hardening, but teaches that "When the
amount of boron is greater than 0.16 part per 100 parts of siloxane
. . . , the additional boron . . . degrades other physical
properties."
[0007] Nitzsche (U.S. Pat. No. 3,050,490) disclosed that adding
boron nitride to hydroxyl enblocked polymeric dimethylsiloxane gum,
forming the mixture into a tape, and pre-vulcanizing that mixture
resulted in a self-adhering tape that could be wound on an object
and vulcanized into a homogeneous, unitary tube. Nitzsche (U.S.
Pat. No. 3,050,491) disclosed that adding 0.001 to 0.1 wt % boric
acid or alkyl borates produced self-adhering material, but teaches
that "Larger quantities of boron compound impede the vulcanization
and depress the physical properties of the ultimate rubber."
Nitzsche (U.S. Pat. No. 3,0705,59) discloses crosslinking agents
that can be used to make silicone rubbers and includes without
comment in a long list of compounds "esters of boric acid."
Nitzsche (U.S. Pat. No. 3,07,0567) then discloses that
incorporating 0.1 to 10 wt % of a complex compound of boric acid
and a polyhydric alcohol in a silicone base can yield self-adhering
tapes that stick to themselves only at elevated temperature.
[0008] In a patent on self-adhering silicone rubber, Nitzsche (U.S.
Pat. No 3,230,121) discloses the use of boron-containing
self-adhering silicone rubber insulating tape to protect hollow
glass articles. He notes that "The silicone rubbers of the present
discovery possess the surprising property that the more violent the
blow, the greater will be the rebound elasticity. They possess this
property in common with the above-mentioned `bouncing putty,` to
which they are chemically related." Nitzsche's comment is made in
the context of protecting glassware from impact and is not
generalized to any other purpose. Moreover, the silicone rubbers
Nitzsche employed in U.S. Pat. No. 3,230,121 are themselves prior
art and Nitzsche provides a comprehensive list of prior art
patents. The most recent of those prior art patents is Nitzsche's
own work: U.S. Pat. No.3,050,491 (listed in U.S. Pat. No. 3,230,121
as "Ser. No. 9,428, filed Feb. 18; 1960"). In U.S. Pat. No.
3,050,491, Nitzsche teaches against using more than 0.1 wt % boron
compounds in silicone elastomers.
[0009] Eisinger (U.S. Pat. No. 3,231,542) discloses
boron-containing self-adhering silicone rubbers with improved
surface characteristics. Fekete (U.S. Pat. No. 3,296,182)
incorporates approximately 0.35 wt % boric acid to silicones, along
with a titanium compound, to'obtain pressure-sensitive adhesive
elastomers. Kelly (U.S. Pat. No. 3,330,797) discloses additional
boron-containing self-adhering silicone elastomers. Foster (U.S.
Pat. No. 3,379,607) added boron compounds to silicones to promote
adhesion to surfaces. Proriol (U.S. Pat. No. 3,629,183) discloses
boron-containing silicones that vulcanize to form adhesive
elastomers on heating. Greenlee (U.S. Pat. No. 3,772,240) found
that adding boric acid to silicones improved their adhesion to
metals. Wegehaupt (U.S. Pat. No. 3,855,171) incorporates
pyrogenically produced mixed oxides of boron and an element
selected from the class consisting of silicon, aluminum, titanium
and iron in silicones for the purposes of preparing either
self-adhering elastomers or bouncing putty.
[0010] Maciejewski (U.S. Pat. No. 4,339,339) recognizes that
bouncing putty's bounciness makes it unable to absorb energy during
sudden impacts. He discloses a boron-containing, non-vulcanizable
silicone for use for hydrostatic damping and shock absorption that
is able to absorb energy during impacts because it does not exhibit
the unusual resiliency of bouncing putty.
SUMMARY OF THE INVENTION
[0011] The invention is directed to viscoelastic silicone rubber
compositions, which are part of a broad class of compounds that
include dense materials, foamed materials, comminuted materials,
and materials that can be molded and even incorporated in other
known materials to form blended materials and composite materials.
These materials are solids in that they have equilibrium shapes to
which they return in the absence of imposed stresses, but they
exhibit time-dependent stiffnesses: they are stiffer at short
timescales than they are at long timescales. A viscoelastic
silicone rubber composition of the invention exhibits a Shore
Hardness that decreases significantly as the duration of the
measurement increases. For example, as shown in FIG. 1 of
International Patent Application No. PCT/US2011/027720, which is
incorporated herein by reference, when a Shore durometer is pressed
against the surface of the rubber, the immediate reading of the
durometer is significantly greater than the reading of that same
durometer after it has been in place for 60 seconds. In other
words, a viscoelastic silicone rubber composition has a greater
Shore Hardness at time zero, t=0, than it does after 60 seconds,
t=60 seconds.
[0012] In one embodiment, the invention provides viscoelastic
silicone rubber compositions that exhibit a high level of
resilience when subjected to a sudden impact, but deform
extensively when subjected to a prolonged stress. For example, a
heavy metal ball dropped on the embodiment will rebound almost to
its original height and leave the embodiment's shape virtually
unchanged. But that same heavy metal ball allowed to rest on the
embodiment for a minute or two will cause the embodiment's surface
to dent significantly. When the ball is subsequently removed from
the embodiment, the dent will gradually disappear from its surface
and the embodiment will return to its original equilibrium
shape.
[0013] Accordingly, in one embodiment, the viscoelastic silicone
rubbers of the invention are stiffer on short timescales than they
are on long timescales. When subjected to brief stresses, the
viscoelastic silicone rubber composition is relatively stiff and
elastic, and it resists changing shapes. When subjected to
sustained stresses, however, it is relatively soft and
accommodating, and it gradually changes shapes. When those stresses
are removed, it gradually returns to its original shape. These
viscoelastic silicone rubbers resist compression set and they are
extremely resilient in response to sudden impacts. They can be
dense rubbers, foam rubbers, and particles.
[0014] In one embodiment, the invention provides a silicone rubber
composition in which some of the crosslinks are permanent and
others of the crosslinks are temporary. Because a fraction of its
crosslinks can come apart and then reform, a viscoelastic silicone
rubber composition of the invention can relax' stress in response
to strain and thus adapt to new shapes. The composition has
sufficient permanent crosslinks, however, to establish a permanent
equilibrium shape to which the composition will eventually return
when not subject to any imposed stress. A viscoelastic silicone
rubber composition has sufficient temporary crosslinks to give the
composition a stiffness that is greater on short timescales than it
is on longer timescales.
[0015] In another embodiment, the invention provides viscoelastic
silicone rubber compositions comprising: (a) at least one
polyorganosiloxane comprising at least one
ethylenically-unsaturated group; (b) optionally at least one
permanent crosslinking agent; and (c) at least one temporary
crosslinking agent; wherein the composition contains sufficient
permanent crosslinks to give the composition an equilibrium shape
and sufficient temporary crosslinks to give the composition a
stiffness that is greater on short timescales than it is on long
timescales. .
[0016] In another embodiment, the invention provides viscoelastic
silicone rubber compositions comprising: (a) at least one branched
polyorganosiloxane; (b) at least one permanent crosslinking agent
present in an amount to provide sufficient permanent crosslinks to
give the composition an equilibrium shape; and (c) at least one
temporary crosslinking agent present in an amount to provide
sufficient temporary crosslinks to give the composition a stiffness
that is greater on short timescales than it is on long
timescales.
[0017] In another embodiment, the invention provides viscoelastic
silicone rubber compositions comprising: (a) at least one
polyorganosiloxane; (b) at least one permanent crosslinking agent
present in an amount to provide sufficient permanent crosslinks to
give the composition an equilibrium shape; (c) at least one
temporary crosslinking agent present in an amount to provide
sufficient temporary crosslinks to give the composition a stiffness
that is greater on short timescales than it is on long timescales;
and (d) at least one softening agent present in an amount
sufficient to make the average lifetime of the temporary crosslink
of shorter duration than the average lifetime of the temporary
crosslink in the absence of the softening agent.
DESCRIPTION OF THE INVENTION
[0018] In one embodiment, the invention provides viscoelastic
silicone rubber (VSR) compositions comprising: (a) at least one
polyorganosiloxane containing at least one
ethylenically-unsaturated group; (b) optionally at least one
permanent crosslinking agent; and (c) at least one temporary
crosslinking agent; wherein the composition contains sufficient
permanent crosslinks to give the composition an equilibrium shape
and sufficient temporary crosslinks to give the composition a
stiffness that is greater on short timescales than it is on long
timescales. Each of these components is discussed below.
[0019] In another embodiment, this invention relates to
viscoelastic silicone rubber compositions comprising: (a) at least
one branched polyorganosiloxane; (b) at least one permanent
crosslinking agent present in an amount to provide sufficient
permanent crosslinks to give the composition an equilibrium shape;
and (c) at least one temporary crosslinking agent present in an
amount to provide sufficient temporary crosslinks to give the
composition a stiffness that is greater on short timescales than it
is on long timescales. Each of these components is discussed
below.
[0020] In another embodiment, the invention provides viscoelastic
silicone rubber compositions comprising: (a) at least one
polyorganosiloxane; (b) at least one permanent crosslinking agent
present in an amount to provide sufficient permanent crosslinks to
give the composition an equilibrium shape; (c) at least one
temporary crosslinking agent, present in an amount to provide
sufficient temporary crosslinks to give the composition a stiffness
that is greater on short timescales than it is on long timescales;
and (d) at least one softening agent present in an amount
sufficient to make the average lifetime of the temporary crosslink
of shorter duration than the average lifetime of the temporary
crosslink in the absence of the softening agent. Each of these
components is discussed below.
[0021] In a VSR composition of the invention, some of the
crosslinks are permanent and others of the crosslinks are
temporary. Because a fraction of its crosslinks can come apart and
then reform, a VSR composition of the invention can relax stress in
response to strain and thus adapt to new shapes. The composition
has sufficient permanent crosslinks, however, to establish a
permanent equilibrium shape to which the composition will
eventually return when not subject to any imposed stress. In other
words, the amount of permanent crosslinks is sufficient to make the
rubber composition a solid. A VSR composition has sufficient
temporary crosslinks to give the composition a stiffness that is
greater on short timescales than it is on longer timescales. If a
force is quickly applied to a VSR composition of the invention, it
feels relatively stiff and undergoes relatively little strain. If
the force is applied for a longer time, however, the composition
feels relatively soft and undergoes relatively substantial strain.
Furthermore, the composition possesses a resilience during impact
that increases with the speed of that impact. When the composition
is struck sharply, it exhibits enhanced stiffness and undergoes
particularly little strain. Moreover, the composition stores the
work done on its surface efficiently and returns nearly all of that
work during the rebound.
[0022] Conventional silicone rubber is a solid formed when
individual chain-like polyorganosiloxane molecules (silicones) are
crosslinked together into an extensive network. The crosslinks have
little effect on the short-range mobilities of the individual
molecular chains since those chains can still slide across one
another at room temperature. However, the crosslinks severely limit
the long-range mobilities of those chains. The vast network of
linkages, loops, and tangles present in a heavily crosslinked
silicone material give that material a fixed equilibrium shape and
render it a solid.
[0023] Prior to crosslinking, a basematerial consisting of
countless individual silicone chains is liquid at room temperature,
although it may be quite viscous. In general, the higher the
average molecular weight of the individual silicone molecules, the
more viscous the liquid. As the extent of crosslinking increases,
the average molecular weight of the individual silicone molecules
increases and branching develops--three or more silicone chains
meeting at a single molecular junction. Loops and tangles also
develop in the collection of crosslinked chains.
[0024] When the extent of crosslinking exceeds a certain level, the
silicone "gels"--it becomes a soft, fragile solid. The network of
crosslinked silicone chains is then so extensive that macroscopic
regions of the material are spanned by crosslinked molecules and
these molecules have limited mobility. To form a robust silicone
rubber, however, crosslinking must continue beyond the gel point.
With additional crosslinking, the silicone rubber becomes stiffer
and stronger, but it also becomes less able to adopt substantially
different shapes. There is a trade-off between the crosslinked
silicone's tendency to maintain a specific equilibrium shape and
its ability to adopt other shapes in response to stresses. Thus a
highly crosslinked silicone rubber is very stiff and it resists
deformation. When a silicone rubber is strained beyond its elastic
limit, that rubber tears. To improve their tear strengths,
virtually all conventional silicone rubbers contain reinforcing
fillers such as fumed silica.
[0025] The VSR compositions of this invention are also crosslinked
structures but differ from conventional silicone rubber
compositions. The VSR compositions of the invention include some
crosslinks that are temporary rather than permanent. In a
conventional silicone rubber, all of the crosslinks are permanent.
A "permanent crosslink" is one that is unlikely to come apart at
ordinary temperatures (generally <50.degree. C.) in an ordinary
amount of time (generally <1 day). One example of a permanent
crosslink between two separate silicone chains is an
-oxygen-silicon-oxygen-bridge that connects two silicon atoms in
separate silicone chains by way of another silicon atom. At
ordinary temperatures, the covalent chemical bonds that hold the
-oxygen-silicon-oxygen-bridge together and link it to the two
chains are extremely unlikely to come apart in an ordinary amount
of time. Because all of its crosslinks are permanent, a fully cured
conventional silicone rubber exhibits virtually no time evolution,
e.g., deformation over time. When subject to constant strain, a
fully cured conventional silicone rubber responds with constant
stress and acts to return itself to its original equilibrium shape
no matter how long that strain continues. The relationship between
stress and strain in a conventional silicone rubber resembles that
of an ordinary spring and is approximately time-independent.
[0026] In the VSR compositions of this invention, some crosslinks
are temporary. A "temporary crosslink" is a crosslink that has a
significant probability of coming apart at ordinary temperatures
(<50.degree. C.) in an ordinary amount of time (<1 day). One
example of a temporary crosslink between two separate silicone
chains is a silicon-oxygen-boron-oxygen-silicon bridge that
connects two silicon atoms in separate silicone chains by way of
the boron atom. These chemical bonds have a substantial probability
of coming apart at ordinary temperatures in an ordinary amount of
time, particularly when there are water, alcohol, and/or carboxylic
acid molecules present in the material. Once a temporary crosslink
has come apart, the boron moiety becomes chemically active again
and can attach itself to a different silicone chain or to the same
silicone chain but after a time when the temporary crosslink has
been broken. For simplicity, and merely to illustrate this while
not being bound to this theory, a temporary crosslink can "open"
(detach from one or more silicone chains) and "close" (attach to
one or more silicone chains) in a relatively short amount of time
(e.g., in milliseconds, seconds, minutes, or hours). The rate at
which the temporary crosslinks open and close may depend on
temperature and the chemical environment near those crosslinks.
[0027] Because some of its crosslinks are temporary, a fully cured
VSR of this invention exhibits time evolution. When subject to a
strain that appears suddenly and then remains constant, the
material initially responds with constant stress. On short
timescales, the material's stiffness depends on both the, permanent
and temporary crosslinks. But as the material's temporary
crosslinks open and close, its network structure evolves and its
stress relaxes. At long time scales, in the limit of infinite time,
the temporary crosslinks relax completely and thus do not
contribute to the material's stress. Since the permanent crosslinks
cannot relax, they continue to contribute to the material's stress
indefinitely. On long timescales, the material's stiffness and
shape depend only on the permanent crosslinks.
[0028] The temporary crosslinks remain important in the strained
but relaxed VSR. The temporary crosslinks do not simply open during
the relaxation process; they close to form new and different
temporary crosslinks. When the strain is suddenly removed from the
material, the formation of new temporary crosslinks produces stress
in the material. In effect, the strained material gradually adapted
to its new strained shape and it acts to oppose a sudden return to
its original equilibrium shape. This new stress gradually relaxes
as the temporary crosslinks open and close, until, over a long time
scale, in the limit of infinite time, the unstrained material
becomes once again free of stress and returns to its original
shape.
[0029] It is useful to view a VSR of this invention as having two
overlapping and possibly interconnected networks: one permanent
and'the other temporary. The permanent network has a fixed topology
and gives the material a permanent equilibrium shape--the shape to
which it will return when free of imposed stress for a sufficient
period of time. When the material is subject to constant strain,
that permanent network produces a constant stress. The temporary
network, however, has a topology that evolves with time and it
relaxes so as to eliminate stress.
[0030] When a VSR has been free of strain for a sufficient time,
the material adopts its equilibrium shape and both of the permanent
and temporary networks are free of stress. The overall material is
then free of both stress and strain.
[0031] VSR compositions of the invention exhibit time-dependent
responses to sudden changes in strain. When an unstressed,
unstrained VSR composition of the invention is subject to a sudden
strain which then remains constant, its permanent crosslink network
responds with a stress that rises suddenly and then remains
constant. In contrast, the material's temporary network responds
with a stress that rises suddenly and then relaxes, ultimately to
zero. When the strained but relaxed material is suddenly returned
to zero strain and then remains at zero strain, its permanent
network responds with stress that drops suddenly to zero and
remains at zero. The material's temporary network, however,
responds once more with a stress that rises suddenly and then
relaxes to zero. In other words, the permanent network acts to
return the material to its equilibrium shape while the temporary
network acts to oppose any rapid change in the material's
shape.
[0032] VSR compositions of the invention also exhibit
time-dependent responses to sudden changes in stress. When an
unstressed, unstrained VSR composition of the invention is subject
to a sudden stress that then remains constant, both its permanent
and temporary network oppose the stress and the material responds
with a small strain. The temporary network, however, gradually
relaxes its opposition to the stress so that the material's strain
increases with time. Eventually, only the permanent network is
opposing the stress and the material reaches a constant large
strain.
[0033] When the stressed but relaxed material is suddenly returned
to zero stress and then remains at zero stress, the two networks
oppose one another. The permanent network acts to return the
material to its equilibrium shape, but the temporary network has
adapted to the new shape and acts to oppose the return to
material's equilibrium shape. The temporary network, once more,
gradually relaxes (the temporary crosslinks open and reform) its
opposition and allows the material to return to its equilibrium
shape.
[0034] To be a solid (i.e., to have a permanent equilibrium shape),
any silicone rubber must have enough permanent crosslinks to
connect the individual silicone chains into macroscopic networks,
so that topology and tangles forever dictate that material's shape.
The VSR compositions of this invention are no exception: they must
have sufficient permanent crosslinks to establish a permanent
equilibrium shape. The VSR compositions of the invention may be
formed into a wide variety of shapes and using the same techniques
as with conventional silicone rubbers. Typically, as is known in
the art, a silicone rubber is shaped by placing an uncured liquid
silicone composition into a mold and then crosslinking that
composition into a solid rubber.
[0035] Once a minimum amount of permanent crosslinking has been
reached, however, additional crosslinks in a VSR composition of the
invention may include further permanent crosslinks or may be all
temporary crosslinks. Additional permanent crosslinks increase both
the short timescale and long timescale stiffnesses of the silicone
rubber, while additional temporary crosslinks increase only the
short timescale stiffnes of a VSR composition of the invention.
[0036] One common approach to forming crosslinks is to add a
crosslinking agent, often in the presence of one or more catalysts.
Catalysts may also assist in the self-crosslinking between
crosslinkable groups on the polyorganosiloxane, without the
addition of a crosslinking agent. Molecules of the crosslinking
agent then attach themselves to one or more of the silicone chains.
A crosslinking molecule that attaches itself to only a single chain
does little to form extended networks. Even a crosslinking molecule
that attaches itself to two chains barely contributes to network
forming. But a crosslinking molecule that attaches itself to three
or more chains contributes significantly to the vast networks
needed to form solids.
[0037] The amount of crosslinking agent needed to transform a
liquid silicone into a solid gel has been determined theoretically
by Flory (Paul J. Flory, J. Phys. Chem. 46, 132 (1942)), Stockmayer
(Walter H. Stockmayer, J. Chem. Phys. 11, 45 (1943)), and others.
For the case where the crosslinking agent attaches itself only to
the ends of the silicone chains, this threshold amount follows a
simple formula. The term "coordination number" denotes the number
of silicone chain ends to which a single molecule of the
crosslinking agent can bind and it is assumed that the crosslinking
agent attaches itself to chain ends with perfect efficiency--i.e.,
that the number of attached chain ends is equal to the number of
crosslinker molecules times the crosslinker's coordination number.
In that case, the gelation threshold is:
attached chain ends total chain ends = 1 ( coordination number - 1
) ##EQU00001##
[0038] For a crosslinking agent that attaches to 3 chains, at least
one half of the chain ends must be attached to crosslinking
molecules before the material can begin to solidify. For a
crosslinking agent that attaches to 4 chains, one third of the
chain ends must be attached. And for a crosslinking agent that
attaches to 21 chains, only 5% of the chain ends must be attached
in order for the material to begin to solidify.
[0039] It is clear that a liquid composed of silicone chains can be
transformed into a solid by attaching a small fraction of the
chains' reactive ends to a crosslinking agent with a large
coordination number. If this crosslinking agent forms permanent
crosslinks, then it will give the material a permanent equilibrium
shape. The remaining reactive chain ends.are still available for
attachment to something else, such as a temporary crosslinking
agent.
[0040] The crosslinking agent may also attach itself to points
along the backbones of the silicone chains and/or to branch points
in branched silicone molecules. However, it is more difficult to
predict the amount of crosslinking agent needed to transform a
liquid silicone into a solid gel under such conditions.
Nonetheless, once that crosslinking agent has formed enough
permanent crosslinks to give the material a permanent equilibrium
shape, any remaining reactive sites on the silicone molecules can
be attached to something else, such as a temporary crosslinking
agent.
Polyorganosiloxanes
[0041] Any polyorganosiloxane having silanol groups at the ends of
polyorganosiloxane chains and/or on the backbones of
polyorganosiloxane chains may be used to prepare a VSR composition
of the invention, including, for example, silanol-terminated
polyorganosiloxanes (STPOS). Polyorganosiloxanes generally exist as
liquids of varying viscosities. Those liquids may be used as the
base material for the preparation of a VSR composition of the
invention or as the base material for the preparation of
partially-crosslinked, branched polyorganosiloxanes that may also
be used for the preparation of a VSR composition of the invention.
"Branched polyorganosiloxanes" includes those polyorganosiloxanes
that have one or more branch points and/or are mixtures
thereof.
[0042] The polyorganosiloxane base which may be used to prepare the
VSR compositions (or partially-crosslinked, branched
polyorganosiloxanes) are preferably those polyorganosiloxane
polymers having primarily methyl groups bound to the silicon atoms
making up the siloxane backbone with hydroxyl groups at the
terminal ends of the siloxane backbone. The base is typically a
liquid polymer composition. The molecular weight of the polymers
may range from about 400 to about 110,000 Daltons and preferably
from about 700 to about 43,500 Daltons and more preferably from
about 1,600 to about 36,000 Daltons. The viscosity of the polymers
may range from about 16 to about 50,000 cSt and preferably from
about 30 to 3,500 cSt and more preferably from about 40 to about
2000 cSt. STPOS, particularly silanol-terminated
polydimethylsiloxane (STPDMS), are commonly used in
condensation-cure silicone rubbers and in the preparation of
ordinary borosilicones. Each STPOS molecule has two silanol groups,
one at each end. Preferred STPOS polymers include:
silanol-terminated polydimethylsiloxanes, formula (I);
silanol-terminated diphenylsiloxane-dimethylsiloxane copolymers,
formula (II); and silanol-terminated poly
trifluoropropylmethylsiloxanes, formula (III). These preferred
STPOS are available from Gelest, Inc. and from Emerald Performance
Materials.
##STR00001##
[0043] In formulas (I), (II), and (III), the variables "m" and "n"
are both 1 or greater and represent the number of the repeating
units in parentheses to give the molecular weight of the particular
polymer. Preferred STPOS are those of formula (I), particularly
those available from Gelest Inc. identified in Table 1 below, and
from Emerald Performance Materials indentified in Table 2
below.
TABLE-US-00001 TABLE 1 Gelest Viscosity Molecular Code (cSt) Weight
% (OH) (OH)-- Eq/kg DMS-S12 16-32 400-700 4.5-7.5 2.3-3.5 DMS-S14
35-45 700-1500 3.0-4.0 1.7-2.3 DMS-S15 45-85 2000-3500 0.9-1.2
0.53-0.70 DMS-S21 90-120 4200 0.8-0.9 0.47-0.53 DMS-S27 700-800
18,000 0.2 0.11-0.13 DMS-S31 1000 26,000 0.1 0.055-0.060 DMS-S32
2000 36,000 0.09 0.050-0.055 DMS-S33 3500 43,500 0.08 0.045-0.050
DMS-S35 5000 49,000 0.07 0.039-0.043
TABLE-US-00002 TABLE 2 Emerald Viscosity Code (cSt) SFR 70 70 SFR
100 100 SFR 750 750 SFR 2000 2,000
[0044] Partial crosslinking of these polyorganosiloxanes,
including, for example, STPDMS fluids, can produce fluids
containing branched siloxane molecules that have 3, 4,5, or more
terminal silanols. These partially crosslinked siloxane fluids can
also contain backbone silanols of coordination number 3 or 4, which
may be used herein to bind together siloxane chains to form
T-branches:
--O--Si(CH.sub.3)(-PDMS-OH)--O--
Q-branches:
[0045] --O--Si(-PDMS-OH).sub.2--O--
and backbone silanol groups (via hydrolysis of the crosslinking
agent):
--O--Si(CH.sub.3)(OH)--O--
and
--O--Si(OH).sub.2--O--
[0046] The extent of the partial crosslinking that occurs depends
on the amount of crosslinking agent used, the presence or absence
of crosslinkable groups in the polyorganosiloxane (e.g., the
silanol groups and the ethylenically-unsaturated groups), the
temperature at which the partial crosslinking occurs, the time
allowed for partial crosslinking, the moisture content of the
mixture, and the presence or absence of catalyst(s) during partial
crosslinking. Partial crosslinking in the presence of moisture
encourages the formation of some backbone silanol groups whereas
partial crosslinking in the absence of moisture (i.e., in carefully
dried materials) encourages the formation of branches.
[0047] Partial crosslinking increases the viscosity of the silicone
fluid significantly. The viscosity increases gradually as molecules
having'two crosslinked STPDMS chains form in the fluid. But as
larger crosslinked molecules (3, 4, 5, or more STPDMS chain's)
become common, the fluid's viscosity increases dramatically.
Partially crosslinked STPDMS fluids become extraordinarily viscous
fluids well before they cross the gelation threshold to form true
solids. By controlling the amount of crosslinking agent and the
conditions under which crosslinking takes place, partially
crosslinked STPDMS fluids can be formed with viscosities ranging
from less than 2 times that of the original STPDMS fluid to 1000 or
more times that of the original STPDMS fluid. Partially crosslinked
STPDMS fluids/semisolids/solids may also be formed in the regimes
below, at, and above the gelation threshold.
[0048] In another embodiment of the invention, branched
polyorganosiloxanes may be formed containing both silanol groups
and ethylenically-unsaturated groups, such as, for example, vinyl
groups by using, for example, vinyltriacetoxysilane (VTAS),
vinyltrimethoxysilane, vinyltrichlorosilane, and/or
vinyltriethoxysilane (VTEOS) as crosslinking agents to partially
crosslink STPDMS molecules. This partial crosslinking places a
vinyl group at each T-branch or backbone silanol group. VTAS is
particularly useful for this purpose because it crosslinks STPDMS
quickly and without the need for a catalyst, especially at
temperatures of 60.degree. C. or more. When the STPDMS has been
carefully dried, partial crosslinking with VTAS can produce
branched polyorganosiloxanes with multiple terminal silanols. Using
these techniques, silicone fluids, semisolids, and solids that have
both silanol groups and ethylenically-unsaturated groups, such as,
for example, vinyl groups, on their molecules may be formed.
Ethylenically-unsaturated groups include any unsaturated chemical
compound containing at least one carbon-to-carbon double bond
(e.g., alkenyl groups, vinyl groups, vinylidene groups, allyl
groups, acrylate groups, methacrylate groups, etc.). U.S. Pat. Nos.
4,360,610 and 5,674,935, the disclosures of which are incorporated
by reference, disclose exemplary structures of and methods of
making silanol-terminated polyorganosiloxanes containing
ethylenically-unsaturated (i.e., vinyl) groups, which may be used
in the invention.
[0049] The ethylenically-unsaturated group content of the
polyorganosiloxane may range from about 0.01 wt % to about 5.0 wt
%, preferably from about 0.02 wt % to about 1.0 wt %, and most
preferably from about 0.04 wt % to about 0.85 wt %, by weight of
the polyorganosiloxane. The silanol content of the
polyorganosiloxarie may range from about 0.03 wt % to about 7.5 wt
%, preferably from about 0.08 wt % to about 4.0 wt %, and most
preferably from about 0.09 wt % to about 2.5 wt %, by weight of the
polyorganosiloxane.
[0050] Partial crosslinking with VTAS proceeds quickly at
temperatures of 100.degree. C. or more. Above 100.degree. C., the
approximate boiling point of water at sea level, water is able to
escape from the silicone fluid rapidly as bubbles of vapor. Partial
crosslinking with VTAS proceeds even more quickly at temperatures
of 118.degree. C. or more. Above 118.degree. C., the approximate
boiling point of acetic acid at sea level, acetic acid is able to
escape from the silicone fluid rapidly as bubbles of vapor.
Partially crosslinking with VTAS proceeds especially quickly at
temperatures of 160.degree. C. or more. See, e.g., Examples 68-73.
Preferably, the partial crosslinking with VTAS is done at
temperatures ranging from about 125 to 140.degree. C. See, e.g.,
Examples 74-77.
[0051] The viscosity of a partially-crosslinked STPDMS silicone
fluid can be increased by the addition of a catalyst(s) and/or
other agent(s) that facilitates homocondensation of silanol groups.
Because homocondensation of silanol groups reduces the number of
silanol groups remaining in the fluid, it increases the effective
fraction of crosslinks of the fluid and causes the fluid to
approach or even exceed the gelation threshold.
[0052] Homocondensation of silanol groups:
HO-PDMS.sub.1-OH+HO-PDMS.sub.2-OH''HO-PDMS.sub.1-O-PDMS.sub.2-OH+H.sub.2-
O
can facilitate the formation of the networks present in a VSR
composition of the invention. By reducing the total number of
silanol groups and therefore the total chain ends, that
homocondensation process effectively increases the ratio of
attached chain ends to total chain ends and increases the level of
the network-formation in the VSR. This homocondensation process can
alter a partially crosslinked network that is below the gelation
threshold and therefore a liquid, so that that network is above the
gelation threshold and therefore a solid.
[0053] Because it raises the level of network formation in
partially-crosslinked silicones, homocondensation of silanol groups
can contribute significantly to the curing and solidification of a
VSR of the invention. When a crosslinking agent binds to silanol
groups, the amount of that crosslinker can be specified in terms of
the percent of initially available silanol groups use to form its
crosslinks. 100% of that crosslinker is thus the amount necessary
to use all of the initially available silanols--it saturates the
silanol. For example, a VSR that originally contains 45%
methyltriethoxysilane (MTEOS) and 35% trimethylborate (TMB) is
seemingly under-saturated and might be expected to retain 20% of
its original silanol groups in their unreacted form. It might also
be expected to be a liquid, since 50% MTEOS is required to reach
the gelation threshold. However, homocondensation of silanols
groups, usually expedited by a catalyst, can eliminate 20% of the
original silanol groups so that the resulting VSR is fully
saturated. Moreover, its effective MTEOS saturation is then 56%,
exceeding the gelation threshold and rendering it a solid. See,
e.g., Examples 37 and 52-60.
[0054] Sulfuric acid, even in minute amounts and even at room
temperature, encourages the homocondensation of silanol groups in
partially-crosslinked STPDMS silicone fluids. Removal of the water
molecules released by homocondensation further encourages
homocondensation. Homocondensation can be terminated by removing or
neutralizing the sulfuric acid. See, e.g., Examples 62-67.
[0055] Vacuum degassing of a partially-crosslinked STPDMS silicone
fluid containing sulfuric acid causes the homocondensation process
to proceed more rapidly. By removing accumulated water molecules,
that vacuum degassing shifts the equilibrium distribution of
silicone molecules in the fluid toward higher molecular weight.
See, e.g., Examples 62, 64, and 65.
Permanent Crosslinking Agents
[0056] One general embodiment of this invention is the combination
of at least one linear and/or branched polyorganosiloxane with two
different crosslinking agents--a permanent crosslinking agent and a
temporary crosslinking agent. The permanent crosslinking agent
forms permanent siloxane and/or carbon crosslinks with the polymers
in the polyorganosiloxane. The temporary crosslinking agent forms
temporary crosslinks with that same polyorganosiloxane. In a VSR
composition of the invention, there must be sufficient permanent
crosslinking agent present to establish a robust permanent network
and give the rubber composition its permanent equilibrium shape.
The amount of temporary crosslinking agent may be varied.
[0057] In VSR compositions of the invention, a permanent crosslink
can be any chemical linkage that permanently connects
polyorganosiloxane chain segments (although a linkage that simply
joins two chain segments so that they form a single longer chain
segment is a "chain extension" rather than a true crosslink). The
conventional curing mechanisms--condensation cure, addition cure,
and peroxide cure--all form such chemical linkages between chain
segments. Additionally, the branched polyorganosiloxanes
effectively have a pre-existing crosslink wherever three or more
chain segments meet at a branch point.
[0058] The invention can make use of any permanent crosslinking
technique or method known in the prior art. In particular, it can
make use of condensation-cure crosslinking, addition-cure
crosslinking, peroxide crosslinking, as well as other known
organo-silicone chemistries, including cures based on isocyanates
and epoxies (see, e.g., Examples 26-28, 33-35, 37, and 48).
[0059] The permanent crosslinks needed to give a VSR its
equilibrium shape and render it a solid can be any of the known
crosslinks between polyorganosiloxanes, including siloxane bridges
(chain-O--Si--O-chain) and carbon bridges (chain-C-chain,
-chain-C--C-chain, chain-C--C--C-chain, etc.). While VSR
compositions of the invention based on the condensation cure
generally rely on siloxane bridges for permanent crosslinks, VSR
compositions of the invention based on the addition cure and on the
peroxide cure frequently rely on carbon bridges for permanent
crosslinks. See, e.g., Examples 26-28 and 33-35.
[0060] The siloxane and carbon bond-forming crosslinking agent may
be any crosslinking agent known in the art to crosslink
polyorganosiloxanes. Depending on the type of cure used (e.g.,
condensation, addition, peroxide), for example, one of skill in the
art would readily know which permanent crosslinking agent is
suitable for creating permanent crosslinks. Suitable siloxane
bond-forming crosslinking agents include, for example,
polydiethoxysilane (PDEOS), polydimethoxysilane, tetramethoxysilane
(TMOS), tetraethoxysilane (TEOS), MTEOS, methyltrimethoxysilane,
tetra-n-propoxysilane, vinyltriacetoxysilane (VTAS),
methyltriacetoxysilane, ethyltriacetoxysilane,
tetrakis(methoxyethoxy)silane, vinyltrichlorosilane,
methyltrichlorosilane, ethyltrichlorosilane, tetrachlorosilane,
polymethylhydrosiloxane (PMHS),
methylhydrosiloxane-dimethylhydrosiloxane copolymer (PMHS-PDMS),
hydride-terminated polymethylhydrosiloxane, and hydride-terminated
methylhydrosiloxane-dimethylhydrosiloxane copolymer. Siloxane
bond-forming crosslinking agents are available from Gelest, Inc.,
Sigma-Aldrich, Alfa-Aesar, and Emerald Performance Materials.
Suitable carbon bond-forming crosslinking agents include, for
example, polymethylhydrosiloxane (PMHS),
methylhydrosiloxane-dimethylhydrosiloxane copolymer (PMHS-PDMS),
hydride-terminated polymethylhydrosiloxane, hydride-terminated
methylhydrosiloxane-dimethylhydrosiloxane copolymer, benzoyl
peroxide, 2,4-dichlorobenzoyl peroxide (DCBP), dicumyl peroxide
(DCP), and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (VX).
Carbon-bond-forming agents are available from Gelest, Inc.,
Sigma-Aldrich, Alfa-Aesar, Arkema, Inc., and Emerald Performance
Materials. The amount of a particular siloxane and/or carbon
bond-forming crosslinking agent used depends upon the number of
functional groups within the crosslinking agent. The amount of the
crosslinking agent must be sufficient to yield a permanent
equilibrium shape but generally in less than the amount sufficient
to react with all of the silanol and carbon groups, so that some
silanol and carbon groups are available to form temporary
crosslinks. The permanent crosslinking agent may be present in the
VSR compositions of the invention in an amount ranging from about
0.02 wt % to 20.0 wt %, such as, for example, from about 0.04 wt %
to about 15.0 wt %, such as, for example, from about 0.08 wt % to
about 8.0 wt %, based on the total weight of the VSR composition.
Preferably, the permanent crosslinking agent may be present in the
VSR compositions of the invention in an amount ranging from about
0.1 wt % to about 5.0 wt %, based on the total weight of the VSR
composition.
[0061] In another embodiment, the permanent crosslinks need not be
formed using a permanent crosslinking agent. Rather, some or all of
the permanent crosslinks creating chemical linkages that
permanently connect polyorganosiloxane chain segments may be formed
through means other than a permanent crosslinking agent. The
permanent crosslinks may be created through the presence of at
least one permanent crosslinkable group present in the
polyorganosiloxane, such as, for example, a polyorganosiloxane
comprising at least one ethylenically-unsaturated group. In the
peroxide cure, for example, a free radical may attack the
carbon-carbon double bond in the ethylenically-unsaturated group
and cause those carbons to grab onto another polyorganosiloxane
chain (e.g., via self-crosslinking). Alternatively, any process
applied to the polyorganosiloxanes that creates permanent
crosslinks between the polyorganosiloxane chains may be used to
make some or all of the permanent crosslinks. For example, the
application of any electromagnetic radiation (e.g., microwave, near
infrared, ultraviolet, x-ray, gamma rays, high-energy gamma rays,
etc.) may cause permanent crosslinks to form between some
polyorganosiloxanes. Any catalyst that causes the
polyorganosiloxanes to form permanent crosslinks, such as, for
example, platinum; may be used to make some or all of the permanent
crosslinks.
[0062] Any combination of the above-mentioned means for creating
permanent crosslinks between polyorganosiloxane chains may be used
in the invention. Thus, any permanent crosslinking agent,
crosslinkable group present in the polyorganosiloxane, process, or
catalyst that produces permanent crosslinks between
polyorganosiloxanes to give the material a permanent equilibrium
shape may be used.
Temporary Crosslinking Agents
[0063] In a VSR composition of the invention, a temporary crosslink
can be any chemical linkage that temporarily connects
polyorganosiloxane chain segments. Temporary crosslinking agents
may be based on boron, tin, titanium, aluminum, zirconium, arsenic,
lead, and phosphorous atoms. In particular, linkages that can serve
as temporary crosslinks in VSR compositions of the invention
include, but are not limited to, -oxygen-boron-oxygen-bridges,
-oxygen-titanium-oxygen-bridges, and
-oxygen-aluminum-oxygen-bridges.
[0064] In a VSR composition of the invention, at least one
boron-containing compound is present in an amount to provide
sufficient temporary crosslinks to give the composition a
resilience during impact that increases with the speed of that
impact. In another VSR composition of the invention, the
composition comprises at least about 0.1 wt % of at least one
boron-containing compound and exhibits a stiffness that is greater
on short timescales than it is on long timescales and a resilience
during impact that increases with the speed of that impact.
[0065] The boron-containing crosslinking agent may be, for example,
boric acid (BA) or a boric acid ester such as TMB, triethyl borate
(TEB), triisopropyl borate (TIB), and tributyl borate. Due to their
chemical structure, boron-containing crosslinking agents have three
functional groups by which to react with the silanol groups in the
polyorganosiloxane. The use of a boron compound as the temporary
crosslinking agent has an additional consequence: this material
embodiment of the invention typically exhibits a remarkably high
stiffness and resiliency in response to sudden impacts.
[0066] In one embodiment, the branched polyorganosiloxanes having
more than two silanol groups can combine with boron compounds to
form novel borosilicones, titanium compounds to form novel
titanosilicones, aluminum compounds to form novel aluminosilicones,
or mixtures thereof (e.g., borotitanosilicones). Borosilicones of
the invention, for example, are less soluble in alcohols and other
solvents than ordinary STPDMS-based borosilicones and that they
retain their viscoelastic properties better than do ordinary
borosilicones when exposed to moisture or liquid water.
[0067] When adding silanol groups to a STPDMS chain, each silanol
group can be placed along the backbone of the polydimethylsiloxane
(PDMS) chain:
--O--Si(CH.sub.3)(OH)--O--
or as a terminal silanol on a branching PDMS chain segment:
--O--Si(CH.sub.3)(-PDMS-OH)--O--
[0068] Both types of additional silanol groups contribute to the
bonding of borosilicones. Branched PDMS molecules that have 3, 4,
5, or more terminal silanols can combine with boron compounds to
form novel borosilicones having greater tensile strengths and more
resistance to solvents than ordinary STPDMS-based
borosilicones.
[0069] In another embodiment, a wide range of linear and/or
branched polyorganosiloxanes having silanol groups and
ethylenically-unsaturated groups on some, most, or all of their
molecules can be combined with a wide range of boron compounds to
form vulcanizable borosilicones--borosilicone compounds that can be
vulcanized (i.e., permanently crosslinked to form solids). In
addition to partially-crosslinked STPDMS fluids, a more general
class of polyorganosiloxanes having both ethylenically-unsaturated
groups and silanol groups along their backbones and/or at their
chain-ends could be synthesized by persons knowledgeable in the
art. Such molecules may be linear or branched and they could have
the ethylenically-unsaturated and silanol groups distributed in
many different ways. Borosilicones formed from these
polyorganosiloxanes may be turned into VSR compositions of the
invention via, for example, the peroxide cure, the addition cure at
room temperature, and the addition cure at elevated
temperature.
[0070] Vulcanizable partially crosslinked borosilicones (VPCBs) may
be prepared from silanol-containing, partially-crosslinked,
branched STPDMS silicones containing ethylenically-unsaturated
groups by reacting them with, for example, trimethyl borate (TMB).
These borosilicones may be vulcanized to form VSR compositions of
the invention via, for example, the peroxide cure, the addition
cure at room temperature, and the addition cure at elevated
temperature.
[0071] As discussed below, the vulcanizable borosilicones may also
be combined with many other materials prior to vulcanization,
notably with reinforcing fillers (e.g.,
hexamethyldisilazane-treated fume silica (TFS) and Garamite 1958
(G1958)), with conventional methyl vinyl silicone fluids and/or
high-temperature vulcanizing silicones (HCR silicones) (e.g.,
Wacker R401/50), and with conventional STPDMS-based borosilicones
(e.g., 100% TMB in 90-120 cSt STPDMS), as well as with combinations
thereof. VSRs of the invention may be formed from those
combinations. These blended materials vulcanize to form VSRs of the
invention with excellent properties. Adding HCR silicone can
greatly increase the maximum elongation, tear resistance, and
tensile strength of the resulting VSR. Adding up to 25 wt % or more
conventional STPDMS-based borosilicones accentuates the difference
between the short timescale stiffness and long timescale stiffness
of the resulting VSR.
[0072] In another embodiment, borosilicones and vinyl-methyl
silicone fluids and/or HCR silicones can be blended together and
then vulcanized, using either the peroxide cure or the addition
cure, to produce VSRs of the invention. The vinyl-methyl silicone
fluids and/or HCR silicones should be at least 10 weight percent of
the blend and preferably at least 25 weight percent of the blend.
The resulting VSRs of the invention have large elongations at break
and are relatively resistant to tearing. See, e.g., Examples 7-13
and 41-43.
[0073] In addition, blends of branched borosilicones with
vinyl-methyl silicone fluids and/or HCR silicones can be vulcanized
by the addition cure or the peroxide cure combined with the
condensation cure. See, e.g., Example 45. These blends can also be
vulcanized into foamed VSR of the invention, using any of the known
techniques for making foamed silicone rubbers and viscoelastic
silicone rubbers. See, e.g., Example 44.
[0074] Blends of (a) branched borosilicones, titanosilicones,
aluminosilicones, and/or mixtures thereof (e.g.,
borotitanosilicones) and (b) conventional vulcanizable silicones
such as HCR compositions and methyl-vinyl silicone fluids can be
vulcanized to produce VSR of the invention. VSR of the invention
may be prepared from these pairings using both the peroxide cure
(e.g., with 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane
(Luperox.RTM. 101) crosslinker and heat).and the addition cure
(e.g., with polymethylhydrosiloxane crosslinkers and
Pt-complex).
[0075] A borosilicone formed from branched polyorganosiloxanes with
more than two silanol groups on some, most, or all of their
molecules can be vulcanized via the condensation reaction. When
suitable catalyst(s) and/or suitable crosslinking agent(s) are
added to the borosilicone, remaining silanol groups in the
borosilicone as well as silanol groups formed via hydrolysis of
-oxygen-boron-oxygen-bridges can condense to form permanent
-oxygen-silicon-oxygen-linkages.
[0076] A partially-crosslinked borosilicone fluid (a close relative
to a VSR in which the permanent network is not quite extensive
enough to give the composition a permanent equilibrium shape) can
be transformed into a VSR through homocondensation of silanol
groups. Generally, this homocondensation is initiated by the
addition of a catalyst and may or may not be accompanied by a
crosslinking agent. For example, adding AMA (AeroMarine Silicone
Accelerator) to a borosilicone based on partially crosslinked
STPDMS can cause that borosilicone to solidify into a VSR. See,
e.g., Example 37.
[0077] Titanium and/or aluminum compounds can substitute for some
or all of the boron compounds as temporary crosslinkers in VSR
compositions of the invention. VSR of the invention using titanium
compounds (e.g., a titanium alkoxides, such as titanium
isopropoxide (TIP), titanium butoxide, titanium methoxide, titanium
ethoxide, and titanium propoxide, titanium
dibutoxide(bis-2,4-pentanedionate), titanium
diisopropoxide(bis-2,4-pentanedionate), titanium
diisopropoxide(bis-ethylacetoacetate), titanium 2-ethylhexoxide,
titanium trimetylsiloxide, polydibutyltitanate, and
diethoxysiloxane-ethyltitanate copolymer) and/or aluminum compounds
(e.g., aluminum alkoxides, such as aluminum propoxide, aluminum
isopropoxide, aluminum butoxide, aluminum methoxide, and aluminum
ethoxide, and diethoxysiloxane-butylaluminate copolymer) as
temporary crosslinkers may be made as well as VSRs using mixtures
of boron, titanium, and/or aluminum compounds as temporary
crosslinkers. In general, any borosilicone or VSR based on boron
can also be formulated using titanium and/or aluminum in place of
some or all of the boron in that material. For example, titanium
bridges (chain-O--Ti--O-chain) and/or aluminum bridges
(chain-O--Al--O-chain) can act as temporary crosslinks between
polyorganosiloxanes and these titanium and/or aluminum bridges can
replace some or all of the boron bridges (chain-O--B--O-chain) in
VSR of the invention. See, e.g., Example 14 and 15.
[0078] A VSR composition of the invention contains both permanent
and temporary crosslinks. For the permanent crosslinking agent, the
minimum amount of crosslinking is set by the need to exceed the
gelation threshold. For the temporary crosslinking agent, however,
the minimum amount is set only by the desired degree of temporary
crosslinking. It is preferable for the temporary crosslinking
agent, possibly assisted by the permanent crosslinking agent, to
use approximately 100% of the silanol groups on the
polyorganosiloxane--that is, to reach approximately 100% saturation
of the silanol groups. That amount is generally at least 0.005 wt
%, or at least 0.1 wt %. Greater amounts of temporary crosslinking
agents may be used and depend upon the composition and properties
desired for the particular VSR composition. The temporary
crosslinking agent may be present in the VSR compositions of the
invention in an amount ranging from about 0.01 wt % to 20.0 wt %,
such as, for example, from about 0.05 wt % to about 15.0 wt %, such
as, for example, from about 0.08 wt % to about 12.0 wt %, based on
the total weight of the VSR composition. Preferably, the temporary
crosslinking agent may be present in the VSR compositions of the
invention in an amount ranging from about 0.1 wt % to about 11.0 wt
%, and, more preferably, from about 0.3 wt % to about 2.5 wt %,
based on the total weight of the VSR composition.
Softening Agents
[0079] The temporary crosslinks, for example, the boron crosslinks
(-oxygen-boron-oxygen-bridges), between branched
polyorganosiloxanes in VSR compositions of the invention can be
extremely long-lived in the absence of reactive chemicals or
chemical groups in the temporary crosslinker-silicone composition
(e.g., boron-silicone composition). For example, an extremely pure
borosilicone composition--one that is essentially free of moisture,
alcohols, carboxylic acids, and silanol groups--exhibits behavior
that is difficult to distinguish from that of a conventionally
crosslinked silicone composition when studied on relatively short
timescales, such as seconds, minutes, hours, or even longer, near
room temperature.
[0080] When there is a complete absence of chemicals that can react
with and thereby open boron bridges
(chain-oxygen-boron-oxygen-chain), the boron-based crosslinks in
VSR compositions of the invention are effectively permanent near
room temperature. Without such boron-bridge-opening-chemicals, the
boron linkages rarely open near room temperature. Therefore, VSR
compositions of the invention that are approximately devoid of
those chemicals are approximately elastic (rather than
viscoelastic) on timescales of 1 minute or less. See, e.g.,
Examples 48 and 59. Elevated temperatures (e.g., 160.degree. C. or
greater), however, can soften these borosilicones, i.e., open the
boron linkages.
[0081] If chemicals (i.e., softening agents) that can open a boron
bridge (chain-oxygen-boron-oxygen-chain) are present, the
boron-based crosslinks in VSR compositions of the invention are
effectively temporary near room temperature. Such
boron-bridge-opening-chemicals include, but are not limited to,
water, alcohols, polyols, silanols, and carboxylic acids. See,
e.g., Examples 1-13, 48, and 60. Thus, in one embodiment, the VSR
compositions of the invention may comprise at least one softening
agent present in an amount sufficient to make the average lifetime
of the temporary crosslink of shorter duration than the average
lifetime of the temporary crosslink in the absence of the softening
agent.
[0082] Including softening agents that are reactive with the
temporary crosslinks, such as, for example, boron crosslinks,
(e.g., moisture, alcohols, carboxylic acids, and unreacted silanol
groups) in a VSR composition hastens stress relaxation in that
composition. Those added chemicals soften the VSR on timescales
that are sensitive to the rate at which the temporary crosslinks
open. At the very shortest timescales, the temporary crosslinks are
so unlikely to open that there is little opening-rate sensitivity.
At the very longest timescales, the temporary crosslinks are so
likely to open that there is again little opening-rate sensitivity.
But at intermediate timescales, wherein the temporary crosslinks
may or may not open to relax stress, increasing the opening rate
with chemicals will increase the probability of stress relaxation
and thereby soften the composition.
[0083] For VSR compositions of the invention to exhibit significant
viscoelasticity on timescales of 1 minute or less, those materials
generally should contain boron-bridge-opening-chemicals so that
those boron-based crosslinks behave as temporary crosslinks. Those
boron-bridge-opening-chemicals may be added explicitly to the VSR
compositions of the invention, before, during, or after curing.
Those boron-bridge-opening softening agents may also be present
naturally in the original chemicals used to form the VSR
compositions of the invention, as impurities or additives in those
chemicals, as reaction or decay products, or in the environments to
which the VSR compositions of the invention are exposed. See, e.g.,
Examples 1-13, 48, and 60.
[0084] Chemicals bearing hydroxyl and carboxyl groups are
particularly effective boron-bridge-opening-chemicals. Water,
alcohols, polyols, silanols, and carboxylic acids are examples of
chemicals bearing hydroxyl and carboxyl groups. See, e.g., Examples
1-13, 48, and 60. For example, alkyl alcohols, alkenyl alcohols,
polyalkenyl alcohols, aryl alcohols, monols, diols, and triols,
each of which containing from 1 to 30 carbon atoms, including their
isomers, may be effective as softening agents. Furthermore, for
example, alkyl carboxylic acids, alkenyl carboxylic acids,
polyalkenyl carboxylic acids, aryl carboxylic acids, mono-, di-,
and tri-carboxylic acids, each of which containing from 1 to 30
carbon atoms, including their isomers, may be effective as
softening agents. Carboxylic acids are particularly effective as
softening agents. Less than 0.1 wt % carboxylic acid can noticeably
reduce the stiffness of a VSR.
[0085] Boron-bridge-opening-chemicals are most effective at
facilitating the opening and closing of boron bridges in VSR
compositions of the invention when those chemicals remain in the
silicone phase--that is, when they do not phase-separate because of
chemical incompatibility or undergo a phase-change to solid or gas.
In other words, a preferred boron-bridge-opening-chemical is one
that (1) is miscible in VSR compositions of the invention, (2) has
a low melting temperature, and (3) has a low vapor pressure. See,
e.g., Examples 1-13, and 60.
[0086] Many primary alcohols and carboxylic acids (i.e.,
hydrocarbons having a single hydroxyl or carboxyl group) are
miscible in silicones and thus satisfy (1). Also, many or most
silicones having one or more silanol (Si-OH), carbinol (C-OH),
and/or carboxyl groups satisfy (1). Examples include primary
alcohols such as, for example, 2-propanol, hexanol, decanol,
2-ethylhexanol, lauryl alcohol, stearyl alcohol, oleyl alcohol, and
isostearyl alcohol, carboxylic acids such as, for example, acetic
acid, 2-ethylhexanoic acid, lauric acid, stearic acid, oleic acid,
and isostearic acid, and silicones such as, for example,
silanol-terminated polydimethylsiloxanes. See, e.g., Examples 1-13,
and 60.
[0087] Satisfying (2) and (3) simultaneously requires more careful
selection of chemicals. That is because lower-molecular-weight
alcohols and carboxylic acids are often liquid at the relevant
temperatures, but have substantial vapor pressures, whereas
higher-molecular-weight alcohols and carboxylic acids are often
solid at the relevant temperatures.
Fortunately,.higher-molecular-weight alcohols and carboxylic acids
that have branched chains and/or carbon-carbon double bonds tend to
be liquid at relevant temperatures yet have low vapor pressures.
Examples include primary alcohols such as, for example,
2-ethylhexanol, oleyl alcohol, linoleyl alcohol, 2-hexyldecanol,
and isostearyl alcohol, and carboxylic acids such as, for example,
2-ethylhexanoic acid, oleic acid, linoleic acid, 2-hexyldecanoic
acid, and isostearic acid. See, e.g., Examples 1-13, and 60.
[0088] Double bonds are chemically fragile and can be damaged by
light and chemicals. In one embodiment, the
boron-bridge-opening-chemicals have no carbon-carbon double bonds
and thus high chemical stability. They are higher-molecular-weight,
fully saturated fatty alcohols and carboxylic acids that are
branched or that are branched with multiple branch-points so that
they remain liquid even at the lowest temperatures to which the
materials of this invention will be subjected and yet have low
vapor pressures. Examples include primary alcohols such as, for
example, 2-ethylhexanol, 2-hexyldecanol, and isostearyl alcohol,
and carboxylic acids such as, for example, 2-ethylhexanoic acid,
2-hexyldecanoic acid, and isostearic acid. See, e.g., Examples
1-13, and 60.
[0089] Examples of isostearyl alcohol and isostearic acid are
available as synthetic products of Nissan Chemical America
Corporation. They remain liquid down to extremely low temperatures
yet have very low vapor pressures. They are odorless, safe, and
miscible with silicones. They diffuse easily into cured VSR
compositions of the invention and do not exude from those VSR of
the invention. The four commercial compounds are:
TABLE-US-00003 Iso-Stearyl Alcohol FO-180 Melting Point:
<-90.degree. C. Boiling Point: 295.degree. C. ##STR00002##
Iso-Stearyl Alcohol FO-180N Melting Point: <-30.degree. C.
Boiling Point: 306.degree. C. ##STR00003## Iso-Stearic Acid Melting
Point: <-70.degree. C. Boiling Point: 311.degree. C.
##STR00004## Iso-Stearic Acid N Melting Point: <-30.degree. C.
Boiling Point: 320.degree. C. ##STR00005##
[0090] Another preferred softening agent that may be included is
unsaturated oleic acid, despite containing a double bond, which
reduces its chemical stability. See, e.g., Examples 1, 2, and
74-77.
[0091] Arizona Chemicals also produces an isostearic acid blend as
their product "Century 1105." Century 1105 is less preferred as a
boron-bridge-opening-chemical because it tends to exude from
finished VSR compositions of the invention and freezes at 4.degree.
C. Nonetheless, this Arizona saturated fatty acid is likely more
chemically stable than the unsaturated oleic acid. See, e.g.,
Example 49.
[0092] While water is not very miscible in VSR compositions of the
invention and has a high vapor pressure, its abundance in the
atmosphere and in some of the environments to which VSR
compositions of the invention are exposed can maintain its
concentration in VSR compositions of the invention so that it acts
as an important boron-bridge-opening-chemical. See, e.g., Example
48. Water may also hydrolyze esters that may have formed in the VSR
of the invention and thus reduce the availability of other
softening agents. By releasing those softening agents from their
ester form, water increases their effectiveness at softening the
VSR.
[0093] Volatile boron-bridge-opening-chemicals are useful during
the preparation and molding of VSR compositions of the invention
and to temporarily reduce the viscosities of borosilicones. By
increasing the rates of opening and closing of the boron-based
temporary crosslinks, these chemicals allow uncured VSR
compositions of the invention to flow more easily through
processing and molding equipment. Once the volatile chemicals have
evaporated, they no longer have any effect on the VSR compositions
of the invention. Similarly, these chemicals reduce the viscosities
of borosilicones only until they evaporate, after which they have
no effect on the borosilicones. See, e.g., Example 46 and 53-60.
For example, acetic acid is particularly effective as a temporary
softening agent that makes compounding, processing, and molding the
constituents of a VSR much easier. See, e.g., Examples 29-32,
41-44, 46, 48, 53-60, and 62. This temporary softening disappears
once the acetic acid has evaporated or otherwise left the finished
VSR.
[0094] The softening agents may be present in any amount sufficient
to make the average lifetime of the temporary crosslink of shorter
duration than the average lifetime of the temporary crosslink in
the absence of the softening agent. For example, the softening
agent may be present in the VSR compositions of the invention in an
amount ranging from about 0.01 wt % to 5.0 wt %, such as, for
example, from about 0.02 wt % to about 4.0 wt %, such as, for
example, from about 0.03 wt % to about 3.0 wt %, based on the total
weight of the VSR composition. Preferably, the softening agent may
be present in the VSR compositions of the invention in an amount
ranging from about 0.05 wt % to about 2.0 wt %, based on the total
weight of the VSR composition. In other cases, the softening agents
may be present in even lower amounts. For example, when atmospheric
water from the environment is used as the softening agent, less
than about 0.01 wt % may be present and still have a softening
effect. Acetic acid may be present in amount less than about 0.01
wt % and still have a softening effect. Heavy acids, such as oleic
acid and isostearic acid, may be present in an amount as high as
about 2.0 wt %, but more preferably, about 1.2 wt %, and even more
preferably, about 0.8 wt % or less, may be used to render a
softening effect.
Catalysts, Moderators, Accelerators, Additives, and Fillers
[0095] In addition to the softening agents mentioned above, the.
VSR compositions of the invention may alsoinclude any catalysts,
moderators, accelerators, additives, and fillers known for use with
silicone rubber compositions such as those discussed above.
Catalysts that may be used in condensation-cure silicones include,
but, are not limited to, tin and titanium catalysts (e.g.,
dibutyldilauryltin, bis(2-ethylhexanoate)tin, titanium
dibutoxide(bis-2,4-pentanedionate), and titanium
diisopropoxide(bis-2,4-pentanedionate)), and associated
accelerators (e.g., AeroMarine Accelerator). Catalysts that may be
used in addition-cure silicones include, but, are not limited to,
platinum and rhodium catalysts (e.g., chloroplatinic acid, Karstedt
catalyst (platinum-divinyltetramethyldisiloxane complex), Ossko
catalyst (platinum carbonyl cyclovinylmethylsiloxane complex),
Lamoreaux catalyst (platinum-octanaldehyde/octanol complex), and
tris(dibutylsulfide)rhodium trichloride)), and associated
moderators (e.g.,1,3-divinyltetramethyldisiloxane,
1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane).
[0096] A condensation-cure catalyst may be present in the VSR
compositions of the invention in an amount ranging from about 0.001
wt % to about 10.0 wt %, such as, for example, from about 0.005 wt
% to about 8.0 wt %, such as, for example, from about 0.01 wt % to
about 6.0 wt %, based on the total weight of the VSR composition.
Preferably, a condensation-cure catalyst may be present in the VSR
compositions of the invention in an amount ranging from about 0.05
wt % to about 4.0 wt %, based on the total weight of the VSR
composition. An addition-cure catalyst may be present in the VSR
compositions of the invention in an amount, based on the catalyst's
precious metal content alone, ranging from about 0.5 ppm to about
500 ppm, such as, for example, from about 1 ppm to about 100 ppm,
such as, for example, from about 2 ppm to about 50 ppm. Preferably,
an addition-cure catalyst may be present in the VSR compositions of
the invention in an amount, based on the catalyst's precious metal
content alone, ranging from a bout 3 ppm to about 30 ppm. The
peroxide crosslinking agent used in peroxide-cure silicones is
normally activated by heat rather than a catalyst, but it is also
possible to include a catalyst to assist the reactions. The
accelerators may be present in the VSR compositions of the
invention in an amount ranging from about 0.01 wt % to 6.0 wt %,
such as, for example, from about 0.02 wt % to about 5.0 wt %, such
as, for example, from about 0.04 wt % to about 4.0 wt %, based on
the total weight of the VSR composition. Preferably, the
accelerator may be present in the VSR compositions of the invention
in an amount ranging from about 0.1 wt % to about 3.3 wt %, based
on the total weight of the VSR composition. The moderators, which
are optional, may be present in the VSR compositions of the
invention in an amount ranging from about 0.001 wt % to 1.0 wt %,
such as, for example, from about 0.005 wt % to about 0.5 wt %, such
as, for example, from about 0.01 wt % to about 0.2 wt %, based on
the total weight of the VSR composition. Preferably, the moderator
may be present in the VSR compositions of the invention in an
amount ranging from about 0.02 wt % to about 0.1 wt %, based on the
total weight of the VSR composition.
[0097] Peroxides, such as, for example, DCP and VX, may be present
in the VSR compositions of the invention in an amount ranging from
about 0.05 wt % to about 5.0 wt %, such as, for example, from about
0.1 wt % to about 4.0 wt %, such as, for example, from about 0.2 wt
% to about 3.0 wt %, based on the total weight of the VSR
composition. Preferably, a peroxide may be present in the VSR
compositions of the invention in an amount ranging from about 0.4
wt % to about 2.0 wt %, based on the total weight of the VSR
composition. One of skill in the art would understand that
peroxides may be considered . either crosslinking agents or as
agents that initiate crosslinking.
[0098] Fillers may be used in an amount up to about 80 wt % of
rubber composition. For example, the filler may be present in the
VSR compositions of the invention in an amount ranging from about
1.0 wt % to 80.0 wt %, such as, for example, from about 2.0 wt % to
about 50.0 wt %, such as, for example, from about 5.0 wt % to about
40.0 wt %, based on the total weight of the VSR composition.
Preferably, the filler may be present in the VSR compositions of
the invention in an amount ranging from about 8.0 wt % to about
30.0 wt %, based on the total weight of the VSR composition. As is
known in the art the amount of filler used will depend on the
particular filler and the desired end use of the VSR composition.
For example, a VSR composition of the invention may contain a
reinforcing filler such as fumed silica or clay particles.
Hexamethylenedisilazane treated fumed silicas from Gelest, Inc.,
and from Cabot Corp. are preferred reinforcing fillers as are the
Garamite clays from Southern Clay Products. Reinforcing fillers may
also include, for example, fumed alumina, fumed titania, calcium
metasilicate, and silicon dioxide. Density-reducing fillers such as
microballoons or microspheres, e.g., Expancel microspheres from
AkzoNobel may also be used. The amount of density-reducing fillers
depends upon the desired density of the final product. Other
traditional fillers such as pigments, insulators, and other
inorganic fillers may be used as known in the art.
[0099] Adding one or more mixed mineral thixotropes (MMTs), such
as, for example, Garamite 1958 or Garamite 2578 (Southern Clay
Products), as an additive to. VSR compositions of the invention
greatly increases the viscosity of uncured VSR compositions of the
invention and renders that fluid thixotropic. MMTs also increase
the tensile strengths and tear strengths of VSR compositions of the
invention when those MMTs are added as reinforcing fillers.
Dispersing additives such as MMTs can be done effectively using an
ordinary blender or immersion blender. The dispersed MMTs (e.g.,
Garamite 1958 or Garamite 2578) acts as reinforcing filler for the
VSR compositions of this invention. For example, adding 5 wt % or
more MMTs, such as Garamite 1958 to STPDMS, may substantially
increase the elastic modulus, viscous modulus, tensile strength,
and tear resistance of VSR compositions of the invention. When MMTs
are added in the amount of 10 weight percent or more, the increases
in tensile strength and tear strength may be very significant. For
example, adding 12.5 wt % or more Garamite 1958 to STPDMS is
particularly effective at increasing the elastic modulus, viscous
modulus, tensile strength, and tear resistance of a VSR composition
of the invention made from that STPDMS.
[0100] MMTs, such as, for example, Garamite 1958 and Garamite 2578,
are most effective at increasing the tensile strength and tear
strength of VSR compositions of the invention when the MMT(s) are
first blended into the silicone base and then heat-treated to
evaporate a substantial fraction of the water present in the
pre-heat-treated blend. The heat-treatment can be done at a
temperature between 50 and 220.degree. C., but is preferably done
at a temperature between 150 and 200.degree. C. Heat-treatment is
particularly effective when the MMT-silicone blend is heated as a
thin layer for between 1 and 20 minutes, so that the water is able
to evaporate easily and thoroughly from the mixture. VSR
compositions of the invention made from MMT-silicone blends that
have, been heat-treated as thin layers at between 150 and
200.degree. C. for between 1 and 20 minutes have particularly large
tensile strengths and tear resistances. See, e.g., Example 2.
[0101] When a blend consisting of MMTs dispersed in STPDMS is
heated as a thin layer to temperatures ranging from 50.degree. C.
to 220.degree. C., moisture is visibly driven out of the blend and
the blend's viscosity and thixotropy both increase substantially.
This heat treatment is particularly effective when care is taken
not to evaporate or sublime a significant fraction of the
quaternary ammonium compound(s) contained in the MMTs. Blending
from 1.2.5 wt % to 20 wt % Garamite 1958 in 90-120 cSt STPDMS and
then heat-treating that blend at 150.degree. C. to 200.degree. C.
produces an exceptionally viscous and thixotropic fluid.
[0102] Heat-treated blends of MMTs in STPDMS produce VSR
compositions of the invention with excellent characteristics and
that heat treatment of a dispersion of MMT in STPDMS can increase
the elastic modulus, viscous modulus, tensile strength, and tear
resistance of the resulting viscoelastic rubber. Heat-treated
blends of 12.5 wt % to 20 wt % Garamite 1958 in 90-120 ca STPDMS
produce VSR compositions of the invention with exceptionally large
elastic moduluses, viscous moduluses, tensile strengths, and tear
resistances. Even when heat-treated blends of MMTs in STPDMS
incorporating other materials, such as plastic microspheres, they
can still form VSR compositions of the invention with increased
elastic moduluses, viscous moduluses, tensile strengths, and tear
resistances.
[0103] Vulcanizable borosilicones of the invention can produce
foamed VSR compositions of the invention when blowing agents, such
as, for example, AkzoNobel Expancels, sodium bicarbonate,
acodicarbonamide, Exocerol.RTM., Hydrocerol.RTM., Nitrosan.RTM.,
dinitropenfamethylenetetramine, p-tolylsulfonylhydrazide,
4,4-oxybis(benzylsulfonylhydrazide), 5-phenyhetrazol, and
p-tolylsulfonylsemicarbazide, are incorporated into them prior to
vulcanization. Those blowing agents can be expanded prior to or
during the vulcanization process. A blowing agent may be present in
the VSR compositions of the invention in an amount ranging from
about 0.01 wt % to 10.0 wt %, such as, for example, from about 0.02
wt % to about 5.0 wt %, such as, for example, from about 0.04 wt %
to about 4.0 wt %, based on the total weight of the VSR
composition. Preferably, a blowing agent may be present in the VSR
compositions of the invention in an amount ranging from about 0.1
wt % to about 3.0 wt %, based on the total weight of the VSR
composition.
[0104] In one embodiment, vulcanizable borbsilicones of the
invention can produce foamed VSR compositions of the invention when
compounds containing hydroxyl group(s) (e.g., water, alcohols,
carboxylic acids, silanols) are incorporated into them prior to
addition-cure vulcanization. Those hydroxyl groups react with
hydrosiloxanes to release hydrogen gas, which foams the VSR, or
esterify to release water, which may then foam the VSR.
[0105] In another embodiment, vulcanizable borosilicones of the
invention can produce foamed VSR compositions of the invention when
a gas (e.g., nitrogen) is dissolved into the borosilicone at high
pressure and that pressure is abruptly released just prior to
vulcanization. The dissolved gas comes out of solution and foams
the VSR.
[0106] Furthermore, microencapsulated permanent crosslinking
agents, peroxides, and/or catalysts can be embedded in the
viscoelastic silicone rubbers of this invention to render them
self-healing. When the silicone rubber of the invention is torn by
impact or excessive strain, the microencapsulated permanent
crosslinking agent and/or catalyst is released locally. That agent
and/or catalyst then forms new permanent crosslinks that bridge the
tear and reestablished the network of permanent crosslinks. This
self-healing process takes advantage of the reactive sites that
appear whenever temporary crosslinks open. Permanent crosslinks
will replace temporary crosslinks in the vicinity of the tear,
healing the tear. It also takes advantage of the fact that the
temporary crosslinks will hold the two sides of the tear together
during the permanent crosslinking process.
Passivating Agents
[0107] The surface of a VSR of the invention can be passivated
(i.e., rendered nonself-sticky) in one of several ways: (1) by
exposing that surface to titanium compounds, such as, for example,
titanium (IV) isopropoxide (see, e.g., Example 47), (2) by exposing
that surface to condensation-cure catalysts such as, for example,
AeroMarine Silicone Accelerator, with or without additional
condensation-cure crosslinking agents, and/or (3) by coating that
surface with condensation-cure silicone rubber formulations such
as, for example, Wacker A07 or Dow Corning 734. Silicone-organic
surfactants that tend to phase separate from silicones can be used
to coat and passivate the surfaces of VSR compositions of the
invention as well. See, e.g., Example 61.
Methods of Preparation
[0108] The VSR compositions may be prepared using the same
techniques known to prepare other silicone rubber compositions. For
example, VSR compositions of the invention can be made using any of
the known silicone crosslinking and curing chemistries, including
condensation cure, addition cure, and peroxide cure silicone
chemistries, as well as all other known organo-silicone
chemistries, including cures based on isocyanates and epoxies. See,
e.g., Examples 26-28 and 33-35. Catalysts and/or peroxides known in
the art may be used and in similar amounts as with other silicone
rubber compositions. Various methods of preparing the VSR
compositions are described in the examples below.
[0109] VSR compositions of the invention that form permanent
crosslinks using the condensation cure can proceed without
catalysts. For example, acetoxy groups bound to silicon atoms can
react with silanol groups in the absence of catalysts. See, e.g.,
Examples 26-28 and 33-35.
[0110] In one method to prepare a VSR composition of the invention,
the polyorganosiloxane base may first be reacted with a temporary
crosslinking agent, such as, for example, a boron-containing
crosslinking agent, under conditions to produce a borosilicone
compound. This establishes the temporary crosslinking network
within the composition. The reaction between the silanol groups and
the boron-containing crosslinking compound is rapid, such that when
the silanol-terminated polyorganosiloxane base is combined with
both crosslinking agents the temporary crosslinking network will
form before the permanent crosslinking network. To establish the
permanent crosslinking network a siloxane and/or carbon
bond-forming crosslinking agent and an optional catalyst are added
to the borosilicone compound to form a mixture. That mixture may
optionally include a filler and/or a solvent for one or more
components. In some instances the borosilicone compound is itself
still a liquid (its gel point is not reached) and the other
reactants can be directly added to the liquid borosilicone
compound. The mixture is then cured under conditions sufficient to
form a VSR composition. The curing step typically takes place in a
mold so that the mixture is placed in a mold and then cured to
establish its permanent equilibrium state. The VSR compounds of the
invention may be molded into any desired shape. Alternatively, and
with the various embodiments mentioned, a VSR composition of the
invention may also be prepared by: combining a silanol-terminated
polyorganosiloxane base with a siloxane and/or carbon bond-forming
crosslinking agent, a catalyst, an optional filler, and an optional
foaming agent to form a mixture; adding a boron-containing
crosslinking agent to the mixture; and curing the mixture under
conditions sufficient to form a VSR composition.
[0111] In another embodiment, two-part RTV and HTV viscoelastic
silicone rubbers can be formulated by separating the chemicals
necessary to form viscoelastic silicone rubbers into two stable
groupings--groupings that do not cure independently and therefore
remain fluid for long periods of time. To form the viscoelastic
silicone rubbers, those two groups are combined so that the curing
reaction can commence, either at room temperature for RTV
formulations or at elevated temperature for HTV formulations.
[0112] Foamed rubber compositions using the VSR compositions of the
invention may also be prepared using techniques known in the art.
For example a foaming agent may be added to the mixture prior to
placing it in a mold or at least prior to curing the mixture.
Alternatively, a pressurized gas such as nitrogen may be injected
into the mixture during the curing step. Foamed rubber compositions
may also be achieved by gas evolution as a by-product of the curing
process. Each of these methods, which are known in the art, is
described in the examples below.
Uses and Applications of Viscoelastic Siloxane Rubber
Compositions
[0113] The VSR compositions of the invention may be used in the
same way and applications as other viscoelastic rubber compositions
such as bouncing putty, viscoelastic urethane foams, and other
known viscoelastic compositions and high-resilience compositions.
Common among the applications and uses of bouncing putty and other
such compositions are time delays, motion rate governors, shock
absorbing devices, motion coupling devices, furniture leveling
devices, adaptive padding, and therapy putties. For a number of
these uses, however, the bouncing putty requires containment to
keep the putty from flowing beyond its intended region--something
that the VSR compositions of the invention do not require. More
specific uses and applications include, but are not limited to,
acoustic coupling devices; arch supports for shoes; body armor;
cargo restrains; cleaning rollers and pads; doorstops; earplugs;
exercise devices; furniture leveling devices; grips for tree
shakers; grips for writing implements; heel stabilizers for shoes;
impact force dispersion devices and equipment; insoles for shoe;
mattresses; momentum dispersion devices and equipment; motion and
intrusion sensors; motion rate governors; orthotics, pads,
separators, and other non-rigid structures for human health and
comfort; padding and support for flooring materials; padding for
bicycle seats; padding for boots; padding for cameras; padding for
crutches; padding for earpieces; padding for firearms; padding for
hearing aids; padding for shoulder straps; padding for sports
equipment; prostheses; physical therapy materials; safety cushions
and pads; seals for sound, heat, and chemicals; shock dispersion
devices and equipment; straps and cords; time delay devices; toys;
vibration, rattling, chattering, buzzing, and motion snubbers;
vibration transducers; and wedges and other retaining devices.
[0114] The VSR compounds of the invention have a tacky surface.
This allows the rubber composition to adhere to another material
such as cloth. The tacky surface of the compounds may also be
passivated by coating the surface with a solution containing a
further amount of a siloxane bond-forming crosslinking agent, such
as TEOS, and a catalyst. The solution may also contain additional
silanol-terminated polyorganosiloxanes. Passivating the surface
layer removes its tackiness.
EXAMPLES
[0115] The materials used in the examples below are listed in Table
3. In the examples below an expression such as "XXX at nn %
saturation" or "nn % XXX," where XXX is a compound that can react
with silanol groups, refers to the amount of XXX added to a
particular silicone blend that is sufficient to bind with nn % of
the silanol groups in that silicone blend. Similarly, the
expression "YYY at nn wt %" or "nn wt % YYY," where YYY is a
compound or material that can be added to a silicone blend, refers
to the amount of YYY added to a particular silicone blend that is
nn % of the initial weight of that silicone blend. Shore Hardness
was measured according to ASTM 2240.
TABLE-US-00004 TABLE 3 PDMS trimethyl-terminated
polydimethylsiloxane fluid STPOS silanol-terminated
polyorganosiloxanes STPDMS silanol-terminated polydimethylsiloxane
fluid 16-32 cSt STPDMS STPDMS having a viscosity of 16-32 cSt
(Gelest DMS-S12) 45-85 cSt STPDMS STPDMS having a viscosity of
45-85 cSt (Gelest DMS-S15) 90-120 cSt STPDMS STPDMS having a
viscosity of 90-120 cSt (Gelest DMS-S21) 700-800 cSt STPDMS STPDMS
having a viscosity of 700-800 cSt (Gelest DMS-S27) 3500 cSt STPDMS
STPDMS having a viscosity of 3500 cSt (Gelest DMS-S33) BA boric
acid, B(OH).sub.3 TMB trimethyl borate, B(OCH.sub.3).sub.3 TIP
titanium(IV) isopropoxide (Alfa/Aesar) PDEOS polydiethoxysilane
(Gelest PSI-021) TEOS tetraethoxysilane (Gelest SIT7110.0) MTEOS
methyltriethoxysilane (Alfa/Aesar) VTAS vinyltriacetoxysilane
(Gelest SIV9098.0) VTEOS Vinyltriethoxysilane (Alfa/Aesar) IP
Isopropanol TFS hexamethyldisilazane-treated fume silica (Gelest
SIS6962.0 of Cab-o-Sil TS- 530) TO tin II octoate (Gelest SNB1100)
AMA AeroMarine Rapid Set Silicone Cure Accelerator (AeroMarine
Products, San Diego, CA). PMHS polymethylhydrosiloxane (Gelest
HMS-991) PMHS-PDMS Polymethylhydrosiloxane-PDMS copolymer (Gelest
HMS-301) copolymer DCP dicumyl peroxide (Gelest SID3379.0) VX
2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (Luperox .RTM. 101)
G1958 Garamite 1958 (Southern Clay Products) ISAlc Iso-Stearic
Alcohol, a highly branched isomer of stearyl alcohol (Nissan
Chemical FO-180) ISA Iso-Stearic Acid, a highly branched isomer of
stearic acid (Nissan Chemical Iso-Stearic Acid) ISAN Iso-Stearic
Acid-N, a branched isomer of stearic acid (Nissan Chemical Iso-
Stearic Acid) Pt 3-3.5% Platinum-divinyltetramethyldisiloxane
complex, Karstedt catalyst (Gelest SIP6830.3) TVTMTS
1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane moderator
(Gelest SID4613.0) Struksilon 8018 silicone-polyether surfactant
(Schill + Seilacher Struksilon 8018)
Example 1
Oleic-Acid-Softened Condensation-Cure VSR Based on 40% TEOS and 65%
TMB in 30 wt % TFS Reinforced 90-120 cSt STPDMS
[0116] 30 wt % TFS was dispersed in 90-120 cSt STPDMS using a
3-roll mill. To 40.0 g of this blend, 0.330 g TMB (65% saturation),
0.667 g AMA (2 wt %), and 0.331 g TEOS (40% saturation) were added.
The mixture was degassed in vacuum, placed in a sheet mold that
measured 3''.times.3''.times.0.1875'', and allowed to cure and dry
for a week at 63.degree. C. in a dehydrator.
[0117] The cured sample was immersed in oleic acid for several
days. When removed and blotted dry, the sample sheet was highly
viscoelastic and very soft. It deformed easily when touched or
squeezed, but recovered completely over a period of seconds. Its
Shore Hardness was determined to be 650 at t=0, 200 at t=5 sec, and
120 at t=60 sec.
Example 2
Oleic-Acid-Softened Condensation-Cure VSR Based on 50% TEOS and 60%
TMB in 12.5 wt % G1958-Reinforced 90-120 cSt STPDMS
[0118] 12.5 wt % G1958 was dispersed in 90-120 cSt STPDMS using an
immersion blender. This blend was then heat-treated as a thin layer
on an aluminum surface for 5 minutes at 180.degree. C. The
resulting blend was extremely viscous and thixotropic.
[0119] To 40.0 g of this blend, 0.352 g TMB (60% saturation), 0.711
g AMA (2 wt %), and 0.441 g TEOS (50% saturation) were added. The
mixture was degassed in vacuum, placed in a sheet mold that
measured 3''.times.3''.times.0.1875'', and allowed to cure and dry
for a week at 63.degree. C. in a dehydrator.
[0120] The fully cured sample was immersed in oleic acid for
several days. When removed and blotted dry, the sample sheet was
highly viscoelastic and very soft. It deformed easily when touched
or squeezed, but recovered almost completely over a period of
seconds. Its Shore Hardness was determined to be 35A, 54O at t=0,
3A, 19O at t=5 sec, and 0A, 9O at t=60 sec.
Example 3
ISAIc-Softened Condensation-Cure VSR Based on 60% MTEOS and 50% TMB
in 15 wt % TFS-Reinforced 90-120 cSt STPDMS
[0121] 15 wt % TFS was dispersed in 90-120 cSt STPDMS using a
3-roll mill. To 40.0 g of this blend, 0.800 g ISAIc (2 wt %), 0.289
g TMB (50% saturation), 0.700 g AMA (2 wt %), and 0.594 g MTEOS
(60% saturation) were added. The mixture was degassed in vacuum,
placed in a sheet mold measuring 3''.times.3''.times.0.1875'', and
allowed to cure for 24 hours at 40.degree. C. in a dehydrator.
[0122] The resulting sheet was highly viscoelastic and medium soft.
Its Shore Hardness was determined to be 22A, 35O at t=0, 12A, 26O
at t=5 sec, and 7A, 21O at t=60 sec. It deformed fairly easily when
touched or squeezed, but recovered completely over a period of
seconds. A steel ball dropped on its surface rebounded almost to
its original height.
Example 4
ISAN-Softened Condensation-Cure VSR Based on 60% MTEOS and 50% TMB
in 15 wt % TFS-Reinforced 90-120 cSt STPDMS
[0123] 15 wt % TFS was dispersed in 90-120 cSt STPDMS, using a
3-roll mill. To 40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.289
g TMB (50% saturation), 0.350 g AMA (1 wt %), and 0.594 g MTEOS
(60% saturation) were added. The mixture was degassed, placed in a
sheet mold measuring 3''.times.3''.times.0.1875'', and allowed to
cure for 24 hours at 40.degree. C. in a dehydrator.
[0124] The resulting sheet was highly viscoelastic and very soft.
Its Shore Hardness was determined to be 38A, 55O at t=0, 20A, 36O
at t=5 sec, and 13A, 29O at t=60 sec. It deformed easily when
touched or squeezed, but recovered completely over a period of
seconds. A steel ball dropped on its surface rebounded almost to
its original height.
Example 5
ISAN-Softened Condensation-Cure VSR Based on 70% MTEOS and 40% TMB
in 20 wt % TFS-Reinforced 700-800 cSt STPDMS
[0125] 20 wt % TFS was dispersed in 700-800 cSt STPDMS using a
3-roll mill. To 40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.051
g TMB (40% saturation), 0.350.g AMA (1 wt %), and 0.154 g MTEOS
(70% saturation) were added. The mixture was degassed in vacuum,
placed in a sheet mold measuring 3''.times.3''.times.0.1875'', and
allowed to cure for 24 hours at 40.degree. C. in a dehydrator.
[0126] The resulting sheet was highly viscoelastic and extremely
soft. Its Shore Hardness was determined to be 22A, 38O at t=0, 12A,
26O at t=5 sec, and 7A, 20O at t=60 sec. It deformed easily when
touched or squeezed, but recovered completely over a period of
seconds. A steel ball dropped on its surface rebounded to a
fraction of its original height.
Example 6
ISAN-Softened Condensation-Cure VSR Based on 70% MTEOS and 40% TMB
in 20 wt % TFS-Reinforced 3500 cSt STPDMS
[0127] 20 wt % TFS was dispersed in 3500 cSt STPDMS using a 3-roll
mill. To 40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.021 g TMB
(40% saturation), 0.350 g AMA (1 wt %), and 0.064 g MTEOS (70%
saturation) were added. The mixture was degassed in vacuum, placed
in a sheet mold measuring 3''.times.3''.times.0.1875'', and allowed
to cure for 24 hours at 40.degree. C. in a dehydrator.
[0128] The resulting sheet was highly viscoelastic and extremely
soft. Its Shore Hardness was determined to be 20O at t=0, 110 at
t=5 sec, and 4O at t=60 sec. It deformed easily when touched or
squeezed, but recovered completely over a period of seconds. A
steel ball dropped on its surface rebounded to a small fraction of
its original height.
Example 7
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
16-32 cSt STPDMS-Based Borosilicone), Blended and Crosslinked using
VX
[0129] ISAN-softened 16-32 cSt STPDMS-based 100%-saturated
borosilicone (Borosilicone A) was made by adding 12.788 g TMB (100%
saturation) and 0.254 g ISAN (0.25 wt %) to 101.441 g 16-32 cSt
STPDMS. The mixture was heated to 150.degree. C. for 3 hours in a
convection oven to evaporate the resulting methanol and further
dried as a thin sheet at 63.degree. C. in a dehydrator
overnight.
[0130] 16.0 g of the softened borosilicone was combined with 16.0 g
of Wacker R401/50 HTV silicone and kneaded together until the
mixture was homogeneous. 0.080 g of VX crosslinker was added and
the mixture was kneaded again until homogeneous. The viscous blend
was squeezed into a Teflon sheet mold, 3''.times.3''.times.0.1875''
deep. The mold was capped with a Teflon sheet and was placed in an
aluminum press. The aluminum press was bolted closed with the help
of a 20 ton hydraulic press. The press and mold assembly were
heated to 165.degree. C. for 30 minutes. After cooling the mold to
room temperature, the finished VSR sample was removed.
[0131] This VSR had a Shore Hardness of 52A, 60O at t=0, 11A, 31O
at t=5 sec, and 4A, 12O at t=60 sec. It could be stretched slowly
to more than 4 times its original width and returned gradually to
its original shape.
Example 8
Peroxide-Cure VSR Based on 60% HTV Silicone and 40% (ISAN Softened
16-32 cSt STPDMS-Based Borosilicone), Blended and Crosslinked using
VX
[0132] 12.8 g of Borosilicone A was combined with 19.2 g of Wacker
R401/50 HTV silicone and kneaded together until the mixture was
homogeneous. 0.096 g of VX crosslinker was added and the mixture
was kneaded again until homogeneous. The viscous blend was squeezed
into a Teflon sheet mold, 3''.times.3''.times.0.1875'' deep. The
mold was capped with a Teflon sheet and placed in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed.
[0133] This VSR had a Shore Hardness of 60A, 70O at t=0, 17A, 42O
at t=5 sec, and 6A, 26O at t=60 sec. It could be stretched slowly
to more than 4 times its original width and returned gradually to
its original shape.
Example 9
Peroxide-Cure VSR Based on 50% HTV Silicone and 50%
(Highly-ISAN-Softened 16-32 cSt STPDMS-Based Borosilicone), Blended
and Crosslinked using VX
[0134] 16.0 g of Borosilicone A was combined with an additional
0.280 g of ISAN, and then with 16.0 g of Wacker R401/50 HTV
silicone. The mixture was kneaded together until it was
homogeneous. 0.080 g of VX crosslinker was added and the mixture
was kneaded again until homogeneous. The viscous blend was squeezed
into a Teflon sheet mold, 3''.times.3''.times.0.1875'' deep, and
the mold was capped with a Teflon sheet and placed in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed.
[0135] This VSR had a Shore Hardness of 40A, 52O at t=0, 5A, 22O at
t=5 sec, and 4A, 11O at t=60 sec. It could be stretched fairly
quickly to more than 4 times its original width and returned
gradually to approximately its original shape.
Example 10
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
90-120 cSt STPDMS-Based Borosilicone), Blended and Crosslinked
using VX
[0136] ISAN-softened 90-120 cSt STPDMS-based 100%-saturated
borosilicone (Borosilicone B) was made by adding 1.723 g TMB (100%
saturation) and 0.261 g ISAN (0.25 wt %) to 104.4 g 90-120 cSt
STPDMS. The mixture was heated to 150.degree. C. for 3 hours in a
convection oven to evaporate the resulting methanol and further
dried as a thin sheet at 63.degree. C. in a dehydrator
overnight.
[0137] 16.0 g of the softened borosilicone was combined with 16.0 g
of Wacker R401/50 HTV silicone and kneaded together until the
mixture was homogeneous. 0.080 g of VX crosslinker was added and
the mixture was kneaded again until homogeneous. The viscous blend
was squeezed into a Teflon sheet mold, 3''.times.3''.times.0.1875''
deep. The mold was capped with a Teflon sheet and placed in an
aluminum press, which was bolted closed with the help of a 20 ton
hydraulic press. The press and mold assembly were heated to
165.degree. C. for 30 minutes. After cooling the mold to room
temperature, the finished VSR sample was removed.
[0138] This VSR had a Shore Hardness of 44O at t=0, 22O at t=5 sec,
and 6O at t=60 sec. It could be stretched slowly to more than 4
times its original width and returned gradually to its original
shape.
Example 11
Peroxide-Cure VSR Based on 60% HTV Silicone and 40% (ISAN-Softened
90-120 cSt STPDMS-Based Borosilicone), Blended and Crosslinked
using VX
[0139] 12.8 g of Borosilicone B was combined with 19.2 g of Wacker
R401/50 HTV silicone and kneaded together until the mixture was
homogeneous. 0.080 g of VX crosslinker was added and the mixture
was kneaded again until homogeneous. The viscous blend was squeezed
into a Teflon sheet mold, 3''.times.3''.times.0.1875'' deep. The
mold was capped with a Teflon sheet and placed in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed.
[0140] This VSR had a Shore Hardness of 27A, 45O at t=0, 11A, 31O
at t=5 sec, and 4A, 17O at t=60 sec. It could be stretched slowly
to more than 4 times its original width and returned gradually to
its original shape.
Example 12
Addition-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
90-120 cSt STPDMS-Based Borosilicone), Blended and Crosslinked
using PMHS-PDMS and Pt
[0141] A moderated platinum solution (Platinum A) was prepared by
dispersing 1 wt % Pt and 2 wt % TVTMTS in 10 cSt PDMS.
[0142] 4.0 g of Borosillcone A was combined with 4.0 g of Wacker
R401/50 HTV silicone and kneaded together until the mixture was
homogeneous. 0.080 g of PMHS-PDMS (200% saturation) and 0.160 g of
Platinum A were added. The mixture was kneaded again until
homogeneous, then squeezed into a 1''.times.1''.times.0.5'' Delrin
mold. An acetate lid was pressed onto the mold. It set overnight
and was fully cured after a week. This VSR had a Shore Hardness of
63A, 73O at t=0, 60A, 67O at t=5 sec, and 39A, 57O at t=60 sec.
Example 13
Addition-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
90-120 cSt STPDMS-Based Borosilicone), Blended and Crosslinked
using PMHS-PDMS and Pt
[0143] A moderated platinum solution (Platinum B) was prepared by
dispersing 1 wt % Pt and 3 wt % TVTMTS in toluene.
[0144] 4.0 g of Borosilicone A was combined with 4.0 g of Wacker
R401/50 HTV silicone and kneaded together until the mixture was
homogeneous. 0.025 g of PMHS-PDMS (<100% saturation) and 0.100 g
of Platinum B were added. The mixture was kneaded again until
homogeneous, and a 20 ton press was used to squeeze the mixture
into a 1.5'' diameter.times.0.1875'' aluminum mold with a Teflon
gasket. The mixture was then cured at 165.degree. C. for 30
minutes. This VSR had a Shore Hardness of 48A, 58O at t=0, 10A, 27O
at t=5 sec, and 2A, 13O at t=60 sec.
Example 14
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (90-120 cSt
STPDMS-based 200%-Saturated Titanosilicone), Blended and
Crosslinked using VX
[0145] 90-120 cSt STPDMS-based 100%-Saturated titanosilicone was
prepared by adding 3.384 g TIP (200% saturation) to 50.0 g 90-120
cSt STPDMS. The mixture was heated to 175.degree. C. for 4 hours in
a convection oven to evaporate the volatile reaction products. The
mixture was further dried as a thin sheet at 63.degree. C. in a
dehydrator overnight.
[0146] 16.0 g of the titanosilicone was combined with 16.0 g of
Wacker R401/50 HTV silicone and kneaded together until the mixture
was homogeneous. 0.080 g of VX crosslinker was added, and the
mixture was kneaded again until homogeneous. The sticky, viscous
blend was squeezed into a Teflon sheet mold,
3''.times.3''.times.0.1875'' deep, and the mold was capped with a
Teflon sheet and placed it in an aluminum press, which was bolted
closed with the help of a 20 ton hydraulic press. The press and
mold assembly were heated to 165.degree. C. for 30 minutes. After
cooling the mold to room temperature, the finished VSR sample was
removed.
[0147] This VSR had a Shore Hardness of 18A, 43O at t=0, 4A, 24O at
t=5 sec, and OA, 10O at t=60 sec. It was stickier than
borosilicone-based VSRs.
Example 15
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
90-120 cSt STPDMS-Based Borotitanosilicone), Blended and
Crosslinked using VX
[0148] ISAN softened 90-120 cSt STPDMS-based 100%-Saturated
borotitanosilicone was made by adding 0.550 g TMB (67% saturation),
0.558 g TIP (33% saturation), and 0.125 g ISAN (0.25 wt %) to 50.0
g 90-120 cSt STPDMS. The mixture was heated to 175.degree. C. for 4
hours in a convection oven to evaporate the volatile reaction
products and further dried as a thin sheet at 63.degree. C. in a
dehydrator overnight.
[0149] To 16.0 g of the borotitanosilicone, 0.050 g TMB (25%
saturation) was added, and the mixture was allowed to dry in the
dehydrator at 63.degree. C. for several hours. The mixture was then
combined with 16.0 g of Wacker R401/50 HTV silicone and kneaded
together until the mixture was homogeneous. 0.080 g of VX
crosslinker was added and the mixture was kneaded again until
homogeneous. The sticky, viscous blend was squeezed into a Teflon
sheet mold, 3''.times.3''.times.0.1875'' deep, and the mold was
capped with a Teflon sheet and placed it in an aluminum press,
which was bolted closed with the help of a 20 ton hydraulic press.
The press and mold assembly were heated to 165.degree. C. for 30
minutes. After cooling the mold to room temperature, the finished
VSR sample was removed.
[0150] This VSR had a Shore Hardness of 14A,.40O at t=0, 3A, 16O at
t=5 sec, and OA, 6O at t=60 sec. It was much stickier than
borosilicone-based VSRs.
Example 16
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (ISAN-Softened
700-800 cSt STPDMS-Based Borosilicone), Blended and Crosslinked
using VX
[0151] ISAN softened 700-800 cSt STPDMS-based 100%-Saturated
borosilicone was made by adding 0.385 g TMB (100% saturation) and
0.250 g ISAN (0.25 wt %) to 100.0 g 700-800 cSt STPDMS. The mixture
was heated to 175.degree. C. for 4 hours in a convection oven to
evaporate the resulting methanol and further dried as a thin sheet
at 63.degree. C. in a dehydrator overnight.
[0152] 16.0 g of the softened borosilicone was combined with 16.0 g
of Wacker R401/60 HTV silicone and kneaded together until the
mixture was homogeneous. 0.080 g of VX crosslinker was added and
the mixture was kneaded again until homogeneous. The viscous blend
was squeezed into a Teflon sheet mold, 3''.times.3''.times.0.1875''
deep. The mold was capped with a Teflon sheet and placed in an
aluminum press, which was bolted closed with the help of a 20 ton
hydraulic press. The press and mold assembly were heated to
165.degree. C. for 30 minutes. After cooling the mold to room
temperature, the finished VSR sample was removed. This VSR had a
Shore Hardness of 22A, 43O at t=0, 5A, 24O at t=5 sec, and 2A, 13O
at t=60 sec.
Example 17
Peroxide-Cure VSR Based on a VPCB (50% TMB and 0.25 wt % ISAN in
50% VTAS-crosslinked 90-120 cSt STPDMS), Blended and Crosslinked
using VX
[0153] A partially crosslinked silicone fluid was made by adding
1.843 g VTAS (50% saturation) and 0.100 g AMA (0.1 wt %) to 100.0 g
90-120 cSt STPDMS. The mixture was stirred vigorous in an open
beaker and allowed to cure for 72 hours, at which time the
viscosity of the partially crosslinked silicone fluid had reached
approximately 600 cSt. To this silicone fluid, 0.250 g ISAN (0.25
wt %) and 0.825 g TMB (50% saturation) were added. The resulting
softened VPCB (vulcanizable partially crosslinked borosilicone) was
allowed to dry at room temperature as a thin sheet for 48
hours.
[0154] To 8.0 g of the VPCB, 0.046 g VX crosslinker was added, and
the mixture was kneaded until homogeneous. The blend was squeezed
into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep, and the
mold was capped with a Teflon sheet and placed it in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold, assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed. This unreinforced VSR had a Shore
Hardness of 45O at t=0, 19O at t=5 sec, and 8O at t=60 sec.
Example 18
Peroxide-Cure VSR Based on a VPCB (60% TMB and 0.25 wt % ISAN in
50% VTEOS-crosslinked 90-120 cSt STPDMS), Blended and Crosslinked
using VX
[0155] A partially crosslinked silicone fluid was made by adding
1.510 g VTEOS (50% saturation) and 0.250 g AMA (0.25 wt %) to 100.0
g 90-120 cSt STPDMS. The mixture was allowed to cure in an open
beaker for 6 days, at which time the partially crosslinked silicone
fluid began to gel slightly. To this silicone fluid, 0.250 g ISAN
(0.25 wt %) and 0.990 g TMB (60% saturation) were added. The
resulting softened but slightly gelled VPCB was allowed to dry at
room temperature as a thin sheet for 1 hour.
[0156] To 8.0 g of the VPCB, 0.052 g VX crosslinker was added, and
the mixture was kneaded until homogeneous. The blend was squeezed
into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep, and the
mold was capped with a Teflon sheet and placed it in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed. This unreinforced VSR had a Shore
Hardness of 30O at t=0, 15O at t=5 sec, and 12O at t=60 sec.
Example 19
Peroxide-Cure VSR Based on a VPCB (12.5 wt % G1958 reinforcement
and 60% TMB in 50% VTAS-crosslinked 90-120 cSt STPDMS), Blended and
Crosslinked using VX
[0157] A partially crosslinked silicone fluid was made by adding
0.718 g AMA (0.1 wt %) and 13.230 g VTAS (50% saturation) to 717.7
g 90-120 cSt STPDMS. The mixture was stirred vigorous in an open
beaker and allowed to cure for 2 hours, at which time the viscosity
of the partially crosslinked silicone fluid had reached
approximately 250 cSt. To 10 g of this silicone fluid, 1.250 g
G1958 (12.5 wt %) was added and the blend was heat-treated as a
thin layer on a 165.degree. C. surface for 5 minutes.
[0158] To 8 g of this heat-treated blend, 0.078.g TMB (50%
saturation) was added and the resulting VPCB was kneaded until
homogeneous and relatively dry. 0.050 g VX crosslinker was added
and the mixture was again kneaded until homogeneous. The blend was
squeezed into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep,
and the mold was capped with a Teflon sheet and placed it in an
aluminum press, which was bolted closed with the help of a 20 ton
hydraulic press. The press and mold assembly were heated to
165.degree. C. for 30 minutes. After cooling the mold to room
temperature, the finished VSR sample was removed. This
G1958-reinforced VSR had a Shore Hardness of 55A, 68O at t=0, 36A,
58O at t=5 sec, and 17A, 34O at t=60 sec.
Example 20
Peroxide-Cure VSR Based on a VPCB (10 wt % TFS reinforcement and
60% TMB in 50% VTAS crosslinked 90-120 cSt STPDMS), Blended and
Crosslinked using VX
[0159] A partially crosslinked silicone fluid was made by adding
0.718 g AMA (0.1 wt %) and 13.230 g VTAS (50% saturation) to 717.7
g 90-120 cSt STPDMS. The mixture was stirred vigorous in an open
beaker and allowed to cure for 24 hours, at which time the
viscosity of the partially crosslinked silicone fluid had reached
approximately 350 cSt. To 425.1 g of this silicone fluid, 41.3 g
Cabot TS-530 TFS (10 wt %) was added and dispersed using a 3-roll
mill.
[0160] To 416.2 g of this TFS-reinforced partially crosslinked
silicone fluid, 1.040 g ISAN (0.25 wt %) and 3.748 g TMB (60%
saturation) were added and the resulting VPCB (VPCB A) was kneaded
until homogeneous and then allowed to dry at room temperature as a
thin sheet for 24 hours.
[0161] To 8.0 g of this VPCB, 0.010 g TMB and 0.040 g VX
crosslinker were added and the mixture was kneaded until
homogeneous. The blend was squeezed into a Teflon disk mold, 1.5''
dia.times.0.1875'' deep, and the mold was capped with a Teflon
sheet and placed it in an aluminum press, which was bolted closed
with the help of a 20 ton hydraulic press. The press and mold
assembly were heated to 165.degree. C. for 30 minutes. After
cooling the mold to room temperature, the finished VSR sample was
removed. This TFS-reinforced VSR had a Shore Hardness of 40O at
t=0, 17O at t=5 sec, and 80 at t=60 sec.
Example 21
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% VPCB (10 wt %
TFS reinforcement and 60% TMB in 50% VTAS crosslinked 90-120 cSt
STPDMS), Blended and Crosslinked using VX
[0162] 4.0 g of VPCB A and 4.0 g of Wacker R401/60 HTV silicone
were combined and kneaded together until the mixture was
homogeneous. To that mixture, 0.040 g VX crosslinker was added and
the mixture was again kneaded until homogeneous. The mixture was
squeezed into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep,
and the mold was capped with a Teflon sheet and placed it in an
aluminum press, which was bolted closed with the help of a 20 ton
hydraulic press. The press and mold assembly were heated to
165.degree. C. for 30 minutes. After cooling the mold to room
temperature, the finished VSR sample was removed. This VSR had a
Shore Hardness of 40A, 60O at t=0, 28A, 46O at t=5 sec, and 21A,
37O at t=60 sec.
Example 22
Peroxide-Cure VSR Based on 25% HTV Silicone and 75% VPCB (10 wt %
TFS reinforcement and 60% TMB in 50% VTAS crosslinked 90-120 cSt
STPDMS), Blended and Crosslinked using VX
[0163] 6.0 g of VPCB A and 2.0 g of Wacker R401/60 HTV silicone
were combined and kneaded together until the mixture was
homogeneous. To that mixture, 0.040 g VX crosslinker was added and
the mixture was again kneaded until homogeneous. The mixture was
squeezed into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep,
and the mold was capped with a Teflon sheet and placed it in an
aluminum press, which was bolted closed with the help of a 20 ton
hydraulic press. The press and mold assembly were heated to
165.degree. C. for 30 minutes. After cooling the mold to room
temperature, the finished VSR sample was removed. This VSR had a
Shore Hardness of 38A, 52O at t=0, 18A, 32O at t=5 sec, and 11A,
23O at t=60 sec.
Example 23
Peroxide-Cure VSR Based on a VPCB (15 wt % TFS Reinforcement and
60% TMB in 50% VTAS-crosslinked 90-120 cSt STPDMS), Blended and
Crosslinked using VX
[0164] A partially crosslinked silicone fluid was made by adding
0.783 g AMA (0.1 wt %) and 14.432 g VTAS (50% saturation) to 782.9
g 90-120 cSt STPDMS. The mixture was stirred vigorous in an open
beaker and allowed to cure for 52 hours, at which time the
viscosity of the partially crosslinked silicone fluid had reached
approximately 1500 cSt. To 774.4 g of this silicone fluid, 116.1 g
Cabot TS-530 IFS (15 wt %) was added and dispersed using a 3-roll
mill.
[0165] To 847.6 g of this TFS-reinforced silicone fluid, 2.119 g
ISAN (0.25 wt %) and 7.300 g TMB (60% saturation) were added and
the resulting VPCB (VPCB B) was kneaded until homogeneous and then
allowed to dry at room temperature as a thin sheet for 24
hours.
[0166] To 8.0 g of this VPCB, 0.042 g VX crosslinker was added and
the mixture was kneaded until homogeneous. The blend was squeezed
into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep, and the
mold was capped with a Teflon sheet and placed it in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed. This TFS-reinforced VSR had a
Shore Hardness of 38A, 48O at t=0, 15A, 27O at t=5 sec, and 9A, 20O
at t=60 sec.
Example 24
Peroxide-Cure VSR Based on a Vulcanizable Partially Crosslinked
Titanosilicone (60% TIP and 0.25 wt % ISAN in 50% VTEOS-Crosslinked
90-120 cSt STPDMS), Blended and Crosslinked using VX
[0167] A partially crosslinked silicone fluid was made by'adding
1.843 g VTAS (50% saturation) and 0.100 g AMA (0.1 wt %) to 100.0 g
90-120 cSt STPDMS. The mixture was stirred vigorously in an open
beaker and allowed to cure for 7 days, at which time the viscosity
of the partially crosslinked, silicone fluid had reached
approximately 500 cSt.
[0168] To 8.3 g of this silicone fluid, 0.200 g TIP (70%
saturation) and 0.020 g ISAN (0.25 wt %) were added. The resulting
softened vulcanizable partially crosslinked titanosilicone (VPCT)
was kneaded until homogeneous and relatively dry.
[0169] To 8.0 g of the VPCT, 0.046 g VX crosslinker was added, and
the mixture was kneaded until homogeneous. The blend was squeezed
into a Teflon disk mold, 1.5'' dia.times.0.1875'' deep, and the
mold was capped with a Teflon sheet and placed it in an aluminum
press, which was bolted closed with the help of a 20 ton hydraulic
press. The press and mold assembly were heated to 165.degree. C.
for 30 minutes. After cooling the mold to room temperature, the
finished VSR sample was removed. This unreinforced VSR had a Shore
Hardness of 25O at t=0, 19O at t=5 sec, and 16O at t=60 sec.
Example 25
Peroxide-Cure Foamed VSR Based on 3 wt % Expancels in a VPCB (15 wt
% TFS reinforcement and 60% TMB in 50% VTAS-Crosslinked 90-120 cSt
STPDMS), Blended and Crosslinked using VX
[0170] 0.120 g Expancels (930 DU 120) and 0.020 g VX crosslinker
were added to 4.0 g of VPCB B. The mixture was kneaded until
homogeneous. The blend was squeezed into a Teflon disk mold, 1.5''
dia.times.0.1875'' deep, and the mold was capped with a Teflon
sheet and placed it in an aluminum press, which was bolted closed.
The press and mold assembly were heated to 165.degree. C. for 30
minutes. After cooling the mold to room temperature, the finished
foamed VSR sample was removed. The density of this foamed
TFS-reinforced VSR was approximately half that of Example 23 and it
had a Shore Hardness of 48O at t=0, 28O at t=5 sec, and 21O at t=60
sec.
Example 26
Addition-Cure VSR Based on a VPCB (100% TMB in 90% VTAS-Crosslinked
700-800 cSt STPDMS), Blended and Crosslinked with PMHSPDMS and
Pt
[0171] A partially crosslinked silicone fluid was made by adding
0.774 g VTAS (90% saturation) dropwise to 100.0 g 700-800 cSt
STPDMS, while stirring vigorously. The mixture was allowed to cure,
without catalyst, for 5 hours and it became extremely viscous.
[0172] To 3.2 g of this partially crosslinked silicone fluid, 0.012
g TMB (100% saturation), 0.030 g of PMHS-PDMS, and 0.005 g of
platinum complex solution (Gelest SIP6830.3) were added. The
mixture was kneaded until homogeneous. It was formed into a block
and allowed to cure overnight at room temperature. It became a VSR
as the result of the addition cure.
Example 27
Peroxide-Cure VSR Based on a VPCB (15 wt % TFS-Reinforcement and
75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS), Blended and
Crosslinked using VX
[0173] A partially crosslinked silicone fluid was made by adding
10.009 g VTAS (40% saturation) to 678.7 g 90-120 cSt STPDMS. Prior
to this addition, the STPDMS was carefully dried and degassed by
stirring it vigorously in vacuum for 40 minutes. The fluid bubbled
rapidly as moisture and other volatiles boiled out of it, but after
40 minutes it stopped bubbling. The VTAS was added to the dried
STPDMS fluid in a nitrogen-filled glove box and the mixture was
returned to vacuum. It was stirred rapidly under vacuum for 5
minutes, when it again stopped bubbling. The mixture was sealed
under an aluminum foil lid and warmed to 60.degree. C. for 18
hours. It was then uncovered and allowed to continue curing at room
temperature for 24 hours. At that time, the fluid's viscosity had
increased to approximately 8,200 cSt, almost 100 times its starting
value.
[0174] To this partially crosslinked STPDMS, 15 wt % TFS was added
and dispersed using a 3-roll mill. To 672.2 g of this reinforced
mixture, 0.292 g of ISAN (0.05 wt %) and 7.237 g of TMB (75%
saturation) were added. The resulting VPCB (VPCB C) was stirred
until homogeneous and then spread out to dry at room temperature as
a thin layer on a polyethylene plate.
[0175] To 8.0 g of this VPCB were added 0.080 g VX (1.0 wt %). The
mixture was kneaded to homogeneity, pressed into a Teflon mold with
a Teflon lid, and baked at 165.degree. C. for 30 minutes. This
TFS-reinforced VSR had a Shore Hardness of 40A, 53 at t=0, 24A, 41O
at t=5 sec, and 17A, 26O at t=60 sec.
Example 28
Peroxide-Cure VSR Based on a VPCB (15 wt % TFS Reinforcement and
150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS), Blended and
Crosslinked using VX
[0176] A partially crosslinked silicone fluid was made by adding
5.239 g VTAS (90% saturation) to 676.7 g 700-800 cSt STPDMS. Prior
to this addition, the STPDMS was carefully dried and degassed by
stirring it vigorously in vacuum for 90 minutes. The fluid bubbled
rapidly as moisture and other volatiles boiled out of it, but after
90 minutes it stopped bubbling. The VTAS was added to the dried
STPDMS fluid in a nitrogen-filled glove box and the mixture was
returned to vacuum. It was stirred rapidly under vacuum for 5
minutes, when it again stopped bubbling. The mixture was sealed
under an aluminum foil lid and warmed to 60.degree. C. for 18
hours. It was then uncovered and allowed to continue curing at room
temperature for 24 hours. At that time, the fluid's viscosity had
increased to approximately 33,000 cSt, almost 50 times its starting
value.
[0177] To this partially crosslinked STPDMS, 15 wt % TFS was added
and dispersed using a 3-roll mill. To 713.8 g of this reinforced
mixture, 0.310 g of ISAN (0.05 wt %) and 3.586 g of TMB (150%
saturation) were added. The resulting VPCB (VPCB D) was stirred
until homogeneous, then spread out to dry at room temperature as a
thin layer on a polyethylene plate.
[0178] To 8.0 g of this VPCB were added 0.040 g VX (0.5 wt %). The
mixture was kneaded to homogeneity, pressed into a Teflon mold with
a Teflon lid, and baked at 165.degree. C. for 30 minutes. This
TFS-reinforced VSR had a Shore Hardness of 28A, 46O at t=0; 19A,
35O at t=5 sec, and 13A, 27O at t=60 sec.
Example 29
Addition-Cure VSR Based on 50% VPCB (15 wt % TFS Reinforcement and
75% TMB in 40% VTAS-crosslinked 90-120 cSt STPDMS), 25% HTV
silicone, and 25% Borosilicone (100% BA in 90-120 cSt STPDMS),
Blended and Crosslinked using PMHS-PDMS and Pt
[0179] A moderated platinum solution (Platinum C) was prepared by
dispersing 5 wt % Pt and 10 wt % TVTMTS in 350 cSt STPDMS.
[0180] 6.0 g of VPCB C were combined with 3.0 g of HTV silicone
(Wacker R401/50), 3.0 g borosilicone (100% BA in 90-120 cSt
STPDMS), and 0.010 g acetic acid. The resulting 50/25/25 blend was
kneaded until homogeneous and then 0.100 g PMHS-PDMS (approximately
100% saturation) and 0.050 g of Platinum C were added. The mixture
was kneaded until homogeneous and then pressed into an aluminum
mold with a Teflon lid. It was heated to 110.degree. C. for 30
minutes and underwent the addition cure. This TFS-reinforced VSR
had a Shore Hardness of 27A, 46O at t=0, 11A, 25O at t=5 sec, and
1A, 10O at t=60 sec.
Example 30
Addition-Cure VSR Based on 50% VPCB (15 wt % TFS Reinforcement and
150% TMB in 90% VTAS-crosslinked 700-800 cSt STPDMS), 25% HTV
Silicone, and 25% Borosilicone (100% BA in 90-120 cSt STPDMS),
Blended and Crosslinked PMHS-PDMS and Pt
[0181] 6.0 g of VPCB D were combined with 3.0 g of HTV silicone
(Wacker R401/50), 3.0 g borosilicone (100% BA in 90-120 cSt
STPDMS), and 0.010 g acetic acid. The resulting 50/25/25 blend was
kneaded until homogeneous and then 0.100 g PMHS-PDMS (approximately
100% saturation) and 0.050 g of Platinum C were added. The mixture
was kneaded until homogeneous and then pressed into an aluminum
mold with a Teflon lid. It was heated to 110.degree. C. for 30
minutes and underwent the addition cure. This TFS-reinforced VSR
had a Shore Hardness of 23A, 40O at t=0, 11A, 26O at t=5 sec, and
2A, 11O at t=60 sec.
Example 31
Addition-Cure Foamed VSR Based on 50% VPCB (15 wt % TFS
Reinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt
STPDMS), 25% HTV silicone, and 25% Borosilicone (100% TMB in 90-120
cSt STPDMS), Blended and Crosslinked using PMHS-PDMS, Water, and
Pt
[0182] 5.5 g of VPCB D were combined with 2.75 g of HTV silicone
(Wacker R401/50), 2.75 g borosilicone (100% TMB in 90-120 cSt
STPDMS), and 0.010 g acetic acid. The resulting 50/25/25 blend was
dried as a thin sheet at 60.degree. C. for 24 hours, then softened
with another 0.015 g acetic acid. To this mixture were added 0.020
g BA, 0.018 g of water, 0.345 g of PMHS-PDMS, and 0.035 g of
Platinum C. The overall mixture was kneaded until homogeneous.
[0183] 5.0 g of this mixture was pressed into an aluminum mold
having a volume of 10 cc and covered with a Teflon cap. The mold
and mixture were heated to 110.degree. C. for 30 minutes. The
resulting foamed TFS-reinforced VSR had a density of approximately
0.75 g/cc (it did not completely fill the mold) and a Shore
Hardness of 35O at t=0, 26O at t=5 sec, and 12O at t=60 sec.
Example 32
Two-Part Addition-Cure VSR Based on 50% VPCB (15 wt % TFS
Reinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt
STPDMS), 25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120
cSt STPDMS), Blended Separately with PMHS-PDMS and Pt and
Crosslinked when Combined
[0184] 4.0 g of VPCB D were combined with 2.0 g of HTV silicone
(Wacker R401/50), 2.0 g borosilicone (100% TMB in 90-120 cSt
STPDMS), and 0.004 g acetic acid. To a 4.0 g portion of the
resulting 50/25/25 blend were added 0.075 g PMHS-PDMS, thereby
forming Part A. To a second 4.0 g portion of the 50/25/25 blend
were added 0.020 g of Platinum C, thereby forming Part B. Each part
was kneaded until homogeneous.
[0185] After 5 days, Part A and Part B remained unchanged. They
were combined and kneaded together carefully. The combined mixture
was pressed into a Teflon mold and heated to 110.degree. C. for 30
minutes. The resulting TFS-reinforced VSR had a Shore Hardness of
43O at t=0, 30O at t=5 sec, and 15O at t=60 sec.
Example 33
Addition-Cure VSR Based on 50% VPCB (15 wt % TFS Reinforcement and
150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS), 25% HTV
Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),
Blended, Softened with ISA, and Crosslinked using PMHS-PDMS and
Pt
[0186] A partially crosslinked silicone fluid was made by adding
7.312 g VTAS (90% saturation) to 850.0 g 700-800 cSt STPDMS. Prior
to this addition, the STPDMS was carefully dried and degassed by
stirring it vigorously in vacuum for 30 minutes. The fluid bubbled
rapidly as moisture and other volatiles boiled out of it, but after
30 minutes it stopped bubbling. The VTAS was added to the dried
STPDMS fluid in a nitrogen-filled glove box and the mixture was
returned to vacuum. It was stirred rapidly under vacuum for 15
minutes, when it again stopped bubbling. The mixture was sealed
under an aluminum foil lid and warmed to 60.degree. C. for 18
hours. It was then uncovered and allowed to cool to room
temperature, where its viscosity was measured to be approximately
45,000 cSt, approximately 60 times its starting value.
[0187] To this partially crosslinked STPDMS, 15 wt % TFS was added
and dispersed using a 3-roll mill. To 931.6 g of this reinforced
mixture, 0.466 g of ISAN (0.05 wt %) and 4.681 g of TMB (150%
saturation) were added. The resulting VPCB (VPCB E) was stirred
until homogeneous, and then spread out to dry for 24 hours at room
temperature as a thin layer on a polyethylene plate.
[0188] To 100.0 g of this VPCB were added 50.0 g of borosilicone
(100% TMB in 90-120 cSt STPDMS) and 50.0 g of HTV silicone (Wacker
R401/50). This resulting 50/25/25 blend (50/25/25 Blend A) was
kneaded until homogeneous and then dried for 24 hours as a thin
sheet at 60.degree. C.
[0189] To 8.0 g of this 50/25/25 blend were added 0.008 g ISA (0.1
wt %) and the softened blend was kneaded until homogenous. Added
then were 0.100 g PMHSPDMS, 0.025 g of Platinum C, and several mg
of red pigment (Smooth-On Silc-Pig Red). The full combination was
kneaded until homogeneous, pressed into a Teflon mold, and heated
to 110.degree. C. for 30 minutes. The resulting red VSR had a Shore
Hardness of 42O at t=0, 24O at t=5 sec, and 15O at t=60 sec.
[0190] To a second 8.0 g portion of the 50/25/25 blend were added
0.016 g ISA (0.2 wt %) and the crosslinking procedure was repeated,
but with green pigment (Smooth-On Silc-Pig Green). The resulting
green VSR had a Shore Hardness of 37O at t=0, 17O at t=5 sec, and
90 at t=60 sec.
[0191] To a third 8.0 g portion of the 50/25/25 blend were added
0.024 g ISA (0.3 wt %) and the crosslinking procedure was repeated,
but with red and blue pigment (Smooth-On Silc-Pig Red and Blue).
The resulting violet VSR had a Shore Hardness of 32O at t=0, 13O at
t=5 sec, and 5O at t=60 sec.
Example 34
[0192] Addition-Cure VSR Based on 50% VPCB (15 wt % TFS
Reinforcement and 75% TMB in 40% VTAS-Crosslinked 90-120 cSt
STPDMS), 25% HTV silicone, and 25% Borosilicone (100% TMB in 90-120
cSt STPDMS), Blended, Softened with ISA, and Crosslinked using
PMHS-PDMS and Pt
[0193] To 100.0 g of VPCB C were added 50.0 g of borosilicone (100%
TMB in 90-120 cSt STPDMS) and 50.0 g of HIV silicone (Wacker
R401/50). This 50/25/25 blend (50/25/25 Blend B) was kneaded until
homogeneous and then dried for 24 hours as a thin sheet at
60.degree. C.
[0194] To 8.0 g of this 50/25/25 blend were added 0.008 g ISA (0.1
wt %) and the softened blend was kneaded until homogenous. Added
then were 0.100 g PMHSPDMS, 0.025 g of Platinum C, and several mg
of blue pigment (Smooth-On Silc-Pig Blue): The full combination was
kneaded until homogeneous, pressed into a Teflon mold, and heated
to 110.degree. C. for 30 minutes. The resulting blue VSR had a
Shore Hardness of 44O at t=0, 24O at t=5 sec, and 15O at t=60
sec.
[0195] To a second 8.0 g portion of the 50/25/25 blend were added
0.016 g ISA (0.2 wt %) and the crosslinking procedure was repeated,
but with orange pigment (Smooth-On Silc-Pig Fluorescent Orange).
The resulting orange VSR had a Shore Hardness of 38O at t=0, 15O at
t=5 sec, and 9O at t=60 sec.
[0196] The VSRs of Example 34 were observed to be more resilient
during impact than the VSRs of Example 33. Specifically, a dropped
1'' diameter steel ball bounced higher from an Example 34 VSR than
from an Example 33 VSR, all else being equal.
Example 35
Addition-Cure VSR Based on 50% VPCB (15 wt % TFS Reinforcement and
75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS), 25% HTV
silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),
Blended, Softened with ISA, and Crosslinked using VX
[0197] To 8.0 g of 50/25/25 Blend B were added 0.008 g ISA (0.1 wt
%) and the softened blend was kneaded until homogenous. Added then
were 0.060 g VX and several mg of white and red pigments (Smooth-On
Silc-Pig White and Red). The full combination was kneaded until
homogeneous, pressed into a Teflon mold, and heated to 165.degree.
C. for 30 minutes. The resulting pink VSR had a Shore Hardness of
47O at t=0, 23O at t=5 sec, and 14O at t=60 sec.
[0198] To a second 8.0 g portion of 50/25/25 Blend B were added
0.016 g ISA (0.2 wt %) and the crosslinking procedure was repeated,
but with white and blue pigments (Smooth-On Silc-Pig White and
Blue). The resulting sky blue VSR had a Shore Hardness of 45O at
t=0, 23O at t=5 sec, and 18O at t=60 sec.
Example 36
[0199] Addition-Cure Foamed VSR Based on 50% VPCB (15 wt % TFS
Reinforcement and 75% TMB in 40% VTAS-crosslinked 90-120 cSt
STPDMS), 25% HTV silicone, and 25% Borosilicone (100% TMB in 90-120
cSt STPDMS), Blended and Crosslinked using PMHS-PDMS and platinum
catalyst and Blown with High-Pressure Nitrogen
[0200] To 8.0 g of 50/25/25 Blend A were added 0.008 g ISA (0.1 wt
%) and the softened blend was kneaded until homogenous. Added then
were 0.100 g PMHS30 PDMS and 0.025 g of Platinum C. The full
combination was kneaded until homogeneous. 2.0 g of this mixture
were formed into a disk and place in a Teflon-coated high-pressure
cell. The cell was filled with nitrogen gas at 1000 psi and this
pressure was maintained for 2.5 hours. At the end of that period,
the pressure was suddenly released and the mixture foamed
immediately. The foamed mixture was heated to 110.degree. C. for 30
minutes. The resulting foamed VSR had a density of approximately
0.2 Wm.
Example 37
Condensation-Cure VSR Based on a VPCB (15 wt % TFS Reinforcement
and 70% TMB in 65% VTAS-Crosslinked 90-120 cSt STPDMS), Blended and
Crosslinked using AMA
[0201] A partially crosslinked silicone fluid was made by adding
19.993 g VTAS (65% saturation) to 834.3 g 90-120 cSt STPDMS. Prior
to this addition, the STPDMS was degassed in vacuum for 3 minutes.
The fluid was allowed to cure uncovered at room temperature for 24
hours, at which time its viscosity had increased to approximately
1000 cSt, approximately 10 times its starting value.
[0202] To this partially crosslinked STPDMS, 15 wt % TFS was added
and dispersed using a 3-roll mill. To 948.8 g of this reinforced
mixture, 0.949 g of ISAN (0.1 wt %) and 9.533 g of TMB (70%
saturation) were added. The resulting VPCB was stirred until
homogeneous, then spread out to dry at room temperature as a thin
layer on a polyethylene plate.
[0203] To 5.0 g of this VPCB were added 0.050 g AMA (1 wt %) and
the blend was kneaded until homogeneous. It was formed into a disk
and placed on a polyethylene sheet to cure for several days. The
resulting VSR had a Shore Hardness of 53O at t=0, 41O at t=5 sec,
and 22O at t=60 sec.
Example 38
Passivation of a VSR with Silicone Sealant (Wacker A07)
[0204] The surface of a self-sticky VSR was coated with a thin
layer of RTV silicone sealant (Wacker A07) and that sealant was
allowed to cure overnight. The sealant formed a tight bond to the
VSR surface and passivated it completely. A 40 wt % solution of
that same sealant in anhydrous toluene worked equally well at
passivating the other side of the same VSR.
Example 39
Passivation of a VSR with a Titanium Isopropoxide Solution
[0205] A 10 wt % solution of TIP in toluene was prepared. The
surface of a self-sticky VSR was coated with a thin layer of that
solution. The VSR almost immediately lost its'stickiness and was
completely passivated. Its surface felt like that of an ordinary
silicone rubber, and it exhibited no self-adhesion.
Example 40
Passivation of a VSR with AMA
[0206] The surface of a self-sticky VSR was coated with a thin
layer of AMA and allowed to cure overnight. The VSR lost its
stickiness and was completely passivated.
Example 41
50% HTV Silicone and 50% 90-120 cSt STPDMS-Based 100%-Saturated
Borosilicone, Softened with Acetic Acid and Crosslinked using
DCP
[0207] A 90-120 cSt STPDMS-Based 100%-Saturated borosilicone was
prepared by dissolving 15.470 g of BA in 172 g of IP and adding the
solution to 1572.8 g of 90-120 cSt STPDMS. This mixture was heated
to 90.degree. C. for 2 days to evaporate the solvent, and volatile
reaction products and form a borosilicone VSR. The resulting
borosilicone VSR was further dried by heating at 180.degree. C. in
a convection oven for 4 hours.
[0208] 6.0 g of this 100% borosilicone was combined with 0.030 g of
acetic acid (0.5 wt %) to obtain a softened. borosilicone. This
softened borosilicone was then blended with 6.0 g of Wacker R401/60
HTV (high-temperature vulcanizing) silicone and 0.360 g of 25% DCP
(3 wt %) peroxide crosslinking agent. The completed mixture was
cured at 165.degree. C. for 60 minutes and became a VSR. The sample
was put in a 200.degree. C. oven for 4 hours as post-cure.
[0209] This VSR exhibited stretched exponeritial stress relaxation
following sudden compressive or tensile strain. Its elastic modulus
was measured to be 72 kPa and its viscous modulus to be 1.0 MPa.
Its Shore Hardness was determined to be 40A, 520 at t=0 and 6A, 220
at t=60 sec.
Example 42
50% HTV Silicone and 50% 16-32 cSt STPDMS-Based 100%-Saturated
Borosilicone, Softened with Acetic Acid and Crosslinked using
DCP
[0210] A 16-32 cSt STPDMS-Based 100%-Saturated borosilicone was
made by adding 1.261 g TMB (100% saturation) to 10 g 16-32 cSt
STPDMS. The mixture was allowed to dry for several days until it
became a solid film. 0.060 g of acetic acid (0.5 wt %) was added to
the solid borosilicone to obtain a softened borosilicone. This
softened borosilicone was then blended with 11.3 g of Wacker
R401/60 HTV (high-temperature vulcanizing) silicone and 0.670 g of
25% DCP (3 wt %) peroxide crosslinking agent. This completed
mixture was cured at 165.degree. C. for 30 minutes, and a VSR was
obtained. The sample was put in a 200.degree. C. oven for 4 hours
as post-cure.
[0211] This VSR exhibited stretched exponential stress relaxation
following sudden compressive or tensile strain. Its elastic modulus
was measured to be 200 kPa and its viscous modulus to be 4.2 MPa.
Its Shore Hardness was determined to be 68A, 72O at t=0 and 12A,
31O at t=60 sec.
Example 43
50% HTV Silicone and 50% 90-120 cSt STPDMS-Based 100%-Saturated
Borosilicone, Softened with Acetic Acid and Crosslinked using
VX
[0212] The same 90-120 cSt STPDMS-Based 100%-Saturated borosilicone
as in Example 41 was prepared. 10.5 g of the 100% borosilicone was
combined with 0.026 g of acetic acid (0.25 wt %) to obtain a
softened borosilicone. This softened borosilicone was then combined
with 10.7 g of Wacker R401/60 HTV (high-temperature vulcanizing)
silicone and 0.107 g VX (0.5 wt %) peroxide crosslinking agent.
This completed mixture was cured at 165.degree. C. for 30 minutes
to obtain a VSR.
[0213] This VSR exhibited stretched exponential stress relaxation
following sudden compressive or tensile strain. Its elastic modulus
was measured to be 93 kPa and its viscous moduli is to be 1.1 MPa.
Its Shore Hardness was determined to be 36A, 48O at t=0 and 7A, 18O
at t=60 sec.
Example 44
2 wt % Expancels in 75% HTV Silicone and 25% 90-120 cSt
STPDMS-Based 100%-Saturated Borosilicone, Softened with Acetic Acid
and Crosslinked using VX
[0214] The same 90-120 cSt STPDMS-Based 100%-Saturated borosilicone
as in Example 41 was prepared. 1.5 g of the 100% borosilicone was
combined with 0.0038 g of acetic acid (0.25 wt %) to obtain a
softened borosilicone. This softened borosilicone was then blended
with 4.5 g of Wacker R401/60 HTV (high-temperature vulcanizing)
silicone, 0.121 g Expancel 930 DU 120 (2 wt %), and 0.032 g VX
(0.54 wt %) peroxide crosslinking agent. This completed mixture was
cured at 165.degree. C. for 15minutes to obtain a VSR.
[0215] This resulting foamed VSR had a low density, was resilient
upon impact, and deformed slowly in response to sustained stress.
Its Shore Hardness was 33A, 46O at t=0 and 22A, 35O at t=60
sec.
Example 45
50% HTV Silicone and 50% RN Borosilicone and VX
[0216] An HTV (high-temperature vulcanizing) silicone and an RN
(room-temperature vulcanizing) borosilicone were blended. Both
types of cures were initiated. 20 wt % TFS in 90-120 cSt STPDMS was
dispersed using a 3-roll mill. 65% Saturation of TMB was added to
this blend, and the volatile components were allowed to evaporate.
10 g of this dried 65% borosilicone was then combined with 0.330 g
of AMA (3.3 wt %), 0.106 g PDEOS (40% Saturation), 0.124 g VX
(>0.54 wt %), and 10 g Wacker. R401/60 HTV silicone. The mixture
cured overnight at 63.degree. C. via a room-temperature
(condensation reaction) cure. The resulting material was a
viscoelastic solid.
[0217] A high-temperature cure was then initiated by heating the
mixture to 165.degree. C. for 15 minutes. The result was a robust
VSR.
[0218] This VSR exhibited stretched exponential stress relaxation
following sudden compressive or tensile strain. Its elastic modulus
was measured to be 760 kPa and its viscous modulus to be 4.0 MPa.
Its Shore Hardness was 60A, 68O at t=0 and 42A, 54O at t=60
sec.
Example 46
45% TEOS and 63% TMB in 30 wt % TFS Reinforced 90-120 cSt
STPDMS
[0219] 30 wt % TFS was dispersed in 90-120 cSt STPDMS using a
3-roll mill. To 13.0 g of this blend, 0.200 g AMA (2 wt %), 0.050 g
acetic acid (0.5 wt %), 0.112 g TEOS (45% Saturation), and 0.104 g
TMB (63% Saturation) were added. The mixture was degassed in
vacuum, placed in a mold, and allowed to cure and dry at 63.degree.
C. in a dehydrator. The resulting material was highly
viscoelastic.
[0220] This VSR exhibited stretched exponential stress relaxation
following sudden compressive or tensile strain. Its elastic modulus
was measured to be 190 kPa and its viscous modulus to be 2.2 MPa.
Its Shore Hardness was 53A, 67O at t=0 and 30A, 45O at t=60
sec.
Example 47
Passivation of a VSR with a Titanium Isopropoxide Solution
[0221] A VSR sample was prepared using the same procedure as
Example 56. This VSR had a somewhat sticky surface and exhibited
strong self-adhesion.
[0222] A 10 wt % solution of TIP in toluene was prepared and a thin
coating of that solution was painted on the surface of the VSR. The
VSR almost immediately lost its stickiness. Its surface felt like
that of an ordinary silicone rubber, and it exhibited no
self-adhesion.
Example 48
50% VPCB, 25% HTV Silicone, and 25% borosilicone, Blended and
Crosslinked using 200% PMHS-PDMS Copolymer and Platinum
Catalyst
[0223] A partially crosslinked silicone fluid was made by adding
5.239 g VTAS (90% Saturation) to 676.7 g 700-800 cSt STPDMS. Prior
to this addition, the STPDMS was carefully dried and degassed by
stirring it vigorously in vacuum for 90 minutes. The fluid bubbled
rapidly as moisture and other volatiles boiled out of it, but after
90 minutes it stopped bubbling. The VTAS was added to the dried
STPDMS fluid in a nitrogen-filled glove box and the mixture was
returned to vacuum. It was stirred rapidly under vacuum for 5
minutes, when it again stopped bubbling. The mixture was sealed
under an aluminum foil lid and warmed to 60.degree. C. for 18
hours. It was then uncovered and allowed to continue curing at room
temperature for 24 hours. At that time, the fluid's viscosity had
increased to approximately 33,000 cSt, almost 50 times its starting
value.
[0224] To this partially crosslinked STPDMS, 15 wt % TFS was added
and dispersed using a 3-roll mill. To 713.8 g of this reinforced
mixture, 0.310 g of ISAN (0.05 wt %) and 3.586 g of TMB (150%
Saturation) were added. The resulting VPCB (VPCB-1) was stirred
until homogeneous, then spread out to dry at room temperature as a
thin layer on a polyethylene plate.
[0225] A moderated platinum solution (Platinum-1) was prepared by
dispersing 5 wt % Pt (3-3.5% Platinum-divinyltetramethyldisiloxane
complex, Karstedt catalyst--Gelest SIP6830.3) and 10 wt % TVTMTS
(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane
moderator--Gelest SID4613.0) in 350 cSt STPDMS.
[0226] To 5.5 g of VPCB-1 were combined with 2.75 g of HTV silicone
(Wacker R401/50), 2.75 g borosilicone (100% BA in 90-120 cSt
STPDMS), and 0.010 g acetic acid. The resulting 50/25/25 blend was
kneaded until homogeneous and then 0.200 g PMHS-PDMS copolymer
(approximately 200% Saturation) and 0.050 g of Platinum-1 were
added. The mixture was kneaded until homogeneous and then pressed
into an aluminum mold with a Teflon lid. It was heated to
110.degree. C. for 30 minutes and underwent the addition cure. It
was removed from its mold and kept at 60.degree. C. for 18 hours to
complete its cure.
[0227] This sample exhibits stretched exponential relaxation, a
form of relaxation first observed by Kohlrausch (Ann. Phys. Leipzig
12, 393 (1847)) and expressed in the formula:
q(t)=q.sub.0 exp[-(t/.tau.).sup.6],
where t is time, q(t) is the physical characteristic being
described by the relaxation, q.sub.0 is that characteristic at time
t=0, .tau. is a characteristic time constant, and 6 is the
stretching exponent and is 0.ltoreq.6.ltoreq.1. For 6=1, this
relaxation process is ordinary exponential relaxation. The as-cured
sample had a characteristic time constant of 481 seconds and a
stretching exponent of 0.29.
[0228] That extremely slow relaxation rate suggests that the
boron-bridge crosslinks in this as-cured sample were more permanent
than temporary. A likely explanation for that result is that the
PMHS-PDMS copolymer, present in substantial excess in the pre-cure
mixture, reacted with virtually all of the hydroxyl, carboxyl, and
silanol groups in the mixture during the addition cure and left the
as-cured sample nearly devoid of reactive groups that could open
the boron-bridge crosslinks. With almost no
boron-bridge-opening-chemicals present, the VSR appeared
approximately elastic on timescales shorter than 1 minute. This
as-cured VSR had a Shore Hardness of 42O at t=0, 42O at t=5 sec,
and 41O at t=60 sec.
[0229] Exposing this sample to 60% relative humidity air at
20.degree. C. for 30 days reduced its characteristic time constant
to 6.6 seconds and increased its stretching exponent of 0.62. This
faster relaxation rate suggests that the boron-bridge crosslinks in
this atmosphere-equilibrated sample are truly temporary. A likely
explanation for that result is that atmospheric moisture diffused
into the sample and acted as a boron-bridge-opening-chemical,
thereby allowing the sample to exhibit viscoelastic behavior on a
timescale shorter than 1 minute. This atmosphere-equilibrated VSR
had a Shore Hardness of 42O at t=0, 32O at t=5 sec, and 19O at t=60
sec.
Example 49
Arizona Century 1105 Softened 60% MTEOS and 50% TMB in 15 wt %
TFS-Reinforced 90-120 cSt STPDMS
[0230] 15 wt % TFS was dispersed in 90-120 cSt STPDMS using a
3-roll mill. To 40.0 g of this blend, 0.800 g Arizona Century 1105
(2 wt %), 0.289 g TMB (50% Saturation), 0.700 g AMA (2 wt %), and
0.594 g MTEOS (60% Saturation) were added. The mixture was degassed
in vacuum, placed in a sheet mold measuring
3''.times.3''.times.0.1875'', and allowed to cure for 24 hours at
60.degree. C. in a dehydrator. This VSR has a somewhat greasy
surface.
Example 50
Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (90-120 cSt
STPDMS-based 200%-Saturated Titanosilicone), Blended and
Crosslinked using VX
[0231] 90-120 cSt STPDMS-based 100%-Saturated titanosilicone was
prepared by adding 3.384 g TIP (200% saturation) to 50.0 g 90-120
cSt STPDMS. The mixture was heated to 175.degree. C. for 4 hours in
a convection oven to evaporate the volatile reaction products. The
mixture was further dried as a thin sheet at 63.degree. C. in a
dehydrator overnight.
[0232] 16.0 g of the titanosilicone was combined with 16.0 g of
Wacker R401/50 HTV silicone and kneaded together until the mixture
was homogeneous. 0.080 g of VX crosslinker was added, and the
mixture was kneaded again until homogeneous. The sticky, viscous
blend was squeezed into a Teflon sheet mold,
3''.times.3''.times.0.1875'' deep, and the mold was capped with a
Teflon sheet and placed it in an aluminum press, which was bolted
closed with the help of a 20 ton hydraulic press. The press and
mold assembly were heated to 165.degree. C. for 30 minutes. After
cooling the mold to room temperature, the finished VSR sample was
removed.
[0233] This VSR had a Shore Hardness of 18A, 43O at t=0, 4A, 24O at
t=5 sec, and OA, 10O at t=60 sec. It was stickier than
borosilicone-based VSRs.
[0234] Example 51 Peroxide-Cure VSR Based on 50% HTV Silicone and
50% (ISAN-Softened 90-120 cSt STPDMS-Based Borotitanosilicone),
Blended and Crosslinked using VX ISAN softened 90-120 cSt
STPDMS-based 100%-Saturated borotitanosilicone was made by adding
0.550 g TMB (67% saturation), 0.558 g TIP (33% saturation), and
0.125 g ISAN (0.25 wt %) to 50.0 g 90-120 cSt STPDMS. The mixture
was heated to 175.degree. C. for 4 hours in a convection oven to
evaporate the volatile reaction products and further dried as a
thin sheet at 63.degree. C. in a dehydrator overnight.
[0235] To 16.0 g of the borotitanosilicone, 0.050 g TMB (25%
saturation) was added, and the mixture was allowed to dry in the
dehydrator at 63.degree. C. for several hours. The mixture was then
combined with 16.0 g of Wacker R401/50 HTV silicone and kneaded
together until the mixture was homogeneous. 0.080 g of VX
crosslinker was added and the mixture was kneaded again until
homogeneous. The sticky, viscous blend was squeezed into a Teflon
sheet mold, 3''.times.3''.times.0.1875'' deep, and the mold was
capped with a Teflon sheet and placed it in an aluminum press,
which was bolted closed with the help of a 20 ton hydraulic press.
The press and mold assembly was heated to 165.degree. C. for 30
minutes. After cooling the mold to room temperature, the finished
VSR sample was removed.
[0236] This VSR had a Shore Hardness of 14A, 40O at t=0, 3A, 16O at
t=5 sec, and OA, 6O at t=60 sec. It was much stickier than
borosilicone-based VSRs.
Example 52
25%, 30%, 35%, 40%,.50%, 60% VTAS in 90-120 cSt STPDMS and 30%,
40%, 50%, 60% MTEOS in 90-120 cSt STPDMS, Blended and Cured with
AMA
[0237] Ten 20 g samples of 90-120 cSt STPDMS were prepared. To
these ten samples were added, respective: 0.184 g VTAS (25%
saturation), 0.221 g VTAS (30% saturation), 0.258 g VTAS (35%
saturation), 0.295 g VTAS (40% saturation), 0.369 g VTAS (50%
saturation), 0.442 g VTAS (60% saturation), 0.170 g MTEOS (30%
saturation), 0.226 g MTEOS (40% saturation), 0.283 g MTEOS (50%
saturation), 0.340 g MTEOS (60% saturation).
[0238] To each of the ten samples, 0.050 g AMA (0.25 wt %) were
added and stirred in carefully. The ten samples were warmed to
60.degree. C. and allowed to cure for approximately 24 hours. All
ten samples cured to form solid silicone elastomers, although the
30% MTEOS and 40% MTEOS samples were quite soft.
[0239] The gelation thresholds for VTAS or MTEOS in STPDMS,
predicted theoretically by Flory (Paul J. Flory, J. Phys. them. 46,
132 (1942)), Stockmayer (Walter H. StockmaW, J. Chem. Phys. 11, 45
(1943)), and others occurs at 50% saturation. That 25% VTAS and 30%
MTEOS were able to cure STPDMS and form solid silicone elastomers
suggests that considerable homocondensation of the STPDMS chains
occurred, perhaps facilitated by the AMA catalyst. By eliminating
many of the silanol groups, this homocondensation increased the
effective saturation levels of VTAS and MTEOS and caused these
samples to exceed the gelation threshold and become solid silicone
elastomers.
Example 53
60% MTEOS and 30%TMB in 15 wt %TFS-Reinforced 90-120 cSt STPDMS
[0240] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 40.0 g of this blend were added one at a
time: <0.020 g pigment, 0.198 TMB (30% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.679 g MTEOS (60% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, poured into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 57O at t=0 and 43O at t=600 sec.
Example 54
55% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cSt
STPDMS
[0241] 15 wt % TF5 (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 40.0 g of this blend were added one at a
time: <0.020 g pigment, 0.231 TMB (35% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.623 MTEOS (55% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, pouring into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 55O at t=0 and 37O at t=600 sec.
Example 55
50% MTEOS and 40% TMB in 15 wt % TFS-Reinforced 90-120 cSt
STPDMS
[0242] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 40.0 g of this blend were added one at a
time: <0.020 g pigment, 0.264 TMB (40% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.566 MTEOS (55% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, poured into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 56O at t=0 and 33O at t=600 sec.
Example 56
45% MTEOS and 45% TMB in 15 wt % TFS-Reinforced 90-120 cSt
STPDMS
[0243] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 40.0 g of this blend were added one at a
time: <0.020 g pigment, 0.297 TMB (45% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.509 MTEOS (45% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, poured into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 54O at t=0 and 28O at t=600 sec.
Example 57
35% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cSt
STPDMS
[0244] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 40.0 g of this blend were added one at a
time: <0.020 g pigment, 0.231 TMB (35% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.396 MTEOS (35% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, poured into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 50O at t=0 and 25O at t=600 sec.
Example 58
60% MTEOS and 30% TMB in 15 wt % TFS-Reinforced 700-800 cSt
STPDMS
[0245] 20 wt % TFS (Gelest) was dispersed in 700-800 cSt STPDMS
using a three-roll mill. To 40.0 g of this blend were added one at
a time: <0.020 g pigment, 0.046 TMB (30% Saturation), 0.040 g
acetic acid (0.1 wt %), 0.159 MTEOS (60% saturation), and 0.400 g
AMA (1 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum, poured into a
sheet mold that measured 3''.times.3''.times.0.1875'' and allowed
to cure and dry for 24 hours at 60.degree. C. in a dehydrator. It
was then removed from its mold. This VSR was kept at 60.degree. C.
for an additional month to ensure that it was completely cured and
dried, and that all the acetic acid had evaporated. It has Shore
Hardness 33O at t=0 and 17O at t=600 sec.
Example 59
60% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cSt
STPDMS
[0246] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 52.0 g of this blend were added one at a
time: <0.020 g pigment, 0.261 TMB (35% Saturation), 0.052 g
acetic acid (0.1 wt %), 0.768 g MTEOS (60% saturation), and 0.400 g
AMA (0.8 wt %). The blend's viscosity increased significantly upon
the addition of TM B, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum and 40 g were
poured into a sheet mold that measured
3''.times.3''.times.0.1875''. The sample was allowed to cure and
dry for 24 hours at 60.degree. C. in a dehydrator. It was then
removed from its mold. This VSR was kept at 60.degree. C. for an
additional month to ensure that it was completely cured and dried,
and that all the acetic acid had evaporated. It has Shore Hardness
58O at t=0, 56O at t=5 sec, 51O at t=60 sec, 42O at t=300 sec, and
36O at t=600 sec.
Example 60
0.1 wt % ISA, 60% MTEOS, and 35% TMB in 15 wt % IFS-Reinforced
90-120 cSt STPDMS
[0247] 15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using
a three-roll mill. To 52.0 g of this blend were added one at a
time: <0.020 g pigment, 0.261 TMB (35% Saturation), 0.052 g
acetic acid (0.1 wt %), 0.768 g MTEOS (60% saturation), and 0.400 g
AMA (0.8 wt %). The blend's viscosity increased significantly upon
the addition of TMB, but decreased significantly upon addition of
the acetic acid. The mixture was degassed in vacuum and 40 g were
poured into a sheet mold that measured 3'' x 3''.times.0.1875''.
The sample was allowed to cure and dry for 24 hours at 60.degree.
C. in a dehydrator. It was then removed from its mold. This VSR was
kept at 60.degree. C. for an additional month to ensure that it was
completely cured and dried, and that all the acetic acid had
evaporated. It has Shore Hardness 580 at t=0, 49O at t=5 sec, 33O
at t=60 sec, 29O at t=300 sec, and 26O at t=600 sec.
Example 61
Passivation of a VSR with a Titanium Isopropoxide Solution
[0248] A 10 g VSR disk, compositionally equivalent to Example 29,
was painted with a thin layer of Struksilon 8018. The painted disk
became relatively non-sticky and would not stick to itself or to
other VSRs. In contrast, an unpainted disk of the same VSR was
somewhat sticky and would stick to itself temporarily.
Example 62
VSR made from Sulfuric-Acid-Treated Partially Crosslinked STPDMS,
using the Peroxide Cure
[0249] A partially crosslinked STPDMS fluid was prepared by
combining 50.0 g of dried 90-120 cSt STPDMS (Gelest DMS-S21) and
0.737 g VTAS. The STPDMS had been dried by heating it to
100.degree. C. and bubbling dry nitrogen through it for 24 hours.
After curing at 60.degree. C. for more than 72 hours, this
partially crosslinked STPDMS fluid was allowed to cool to room
temperature. It remained a low-viscosity liquid.
[0250] To 7.0 g of that fluid was added approximately 1 mg of
sulfuric acid. The mixture was stirred vigorously under vacuum and
its viscosity began to increase. When its viscosity had reached
approximately 15,000 cSt, 0.116 g of TMB (100% saturation) were
added and the fluid became a borosilicone. After kneading the
borosilicone in a slip roll, it was allowed to dry overnight.
[0251] To the 7.0 g of borosilicone were added 0.007 g iso-stearic
acid (0.1 wt %), 0.007 g acetic acid (0.1 wt %), and 0.070 g VX
(1.0 wt %). After kneading to homogeneity, the blend was pressed
into a Teflon disk mold and vulcanized at 165.degree. C. for 30
minutes. The resulting disk was .a VSR.
Example 63
VPCB with 0.1M Vinyl Groups per Kilogram made from
Sulfuric-Acid-Treated Partially Crosslinked STPDMS
[0252] A partially crosslinked STPDMS fluid was prepared by
combining 500.0 g of dried 90-120 cSt STPDMS (Gelest DMS-S21) and
11.613 g VTAS. The STPDMS had been dried by degassing it in vacuum
for 20 minutes. The fluid was allowed to cure in a sealed container
for 7 days at 60.degree. C. and then . cooled to room temperature.
Its finished viscosity was approximately 420 cSt.
[0253] A 5% dispersion of 0.250 g sulfuric acid in 5.0 g of 350 cSt
PDMS silicone fluid was prepared. Rapid shaking resulted in
microscopic droplets of sulfuric acid suspended in the silicone
fluid.
[0254] To 50.0 g of the partially crosslinked STPDMS was added
0.044 g of the 5% sulfuric acid dispersion. The mixture was stirred
carefully and its viscosity monitored at approximately 30 minute
intervals. After 228 minutes, its viscosity had increased to
approximately 8100 cSt. To this thickened fluid was added 0.020 g
of precipitated calcium carbonate powder (Solvay Winnofil SPM). The
mixture was stirred carefully to facilitate neutralization of the
sulfuric acid.
[0255] To the fluid were added 1.5 g of TMB. When stirred, this
mixture immediately thickened into a borosilicone putty. The
density of vinyl groups in this VPCB is approximately 0.1 M/kg.
Example 64
VPCB with 0.075M Vinyl Groups per Kilogram made from
Sulfuric-Acid-Treated Partially Crosslinked STPDMS
[0256] A partially crosslinked STPDMS fluid was prepared by
combining 500.0 g of dried 90-120 cSt STPDMS (Gelest DMS-S21) and
8.710 g VTAS. The STPDMS had been dried by degassing it in vacuum
for 20 minutes. The fluid was allowed to cure in a sealed container
for 7 days at 60.degree. C. and then cooled to room temperature.
Its finished viscosity was approximately 160 cSt.
[0257] To 50.0 g of the partially crosslinked STPDMS was added
0.043 g of the 5% sulfuric acid dispersion from Example 63. The
mixture was stirred carefully and its viscosity monitored at
approximately 30 minute intervals. After 191 minutes, its viscosity
had increased to approximately 840 cSt and was no longer changing.
The was then vacuum degassed and its viscosity began to increase
rapidly. After 2 hours in vacuum, its viscosity had reached 12,800
cSt. To this thickened fluid was added 0.020 g of precipitated
calcium carbonate powder (Solvay Winnofil SPM). The mixture was
stirred carefully to facilitate neutralization of the sulfuric
acid.
[0258] To the fluid was added 0.50 g of TMB. When stirred, this
mixture immediately thickened into a borosilicone putty. The
density of vinyl groups in this VPCB is approximately 0.075
M/kg.
Example 65
VPCB with 0.05M Vinyl Groups per Kilogram made from
Sulfuric-Acid-Treated Partially Crosslinked STPDMS
[0259] A partially crosslinked STPDMS fluid was prepared by
combining 500.0 g of dried 90-120 cSt STPDMS (Gelest DMS-S21) and
5.807 g VTAS. The STPDMS had been dried by degassing it in vacuum
for 20 minutes. The fluid was allowed to cure in a sealed container
for 7 days at 60.degree. C. and then cooled to room temperature.
Its finished viscosity was approximately 100 cSt.
[0260] To 50.0 g of the partially crosslinked STPDMS was added
0.043 g of the 5% sulfuric acid dispersion from Example 63. The
mixture was stirred carefully and its viscosity monitored at
approximately 30 minute intervals. After 187 minutes, its viscosity
had increased to approximately 360 cSt and was no longer changing.
The fluid was then vacuum degassed and its viscosity began to
increase rapidly. After 3 hours in vacuum, its viscosity had
reached 11,100 cSt. To this thickened fluid was added 0.020 g of
precipitated calcium carbonate powder (Solvay Winnofil SPM). The
mixture was stirred carefully to facilitate neutralization of the
sulfuric acid.
[0261] To the fluid was added 0.40 g of TMB. When stirred, this
mixture immediately thickened into a borosilicone putty. The
density of vinyl groups in this VPCB is approximately 0.05
M/kg.
Example 66
VPCB with 0.033M Vinyl Groups per Kilogram made from
Sulfuric-Acid-Treated Partially Crosslinked STPDMS
[0262] A partially crosslinked STPDMS fluid was prepared by
combining 100.0 g of dried 90-120 cSt STPDMS (Gelest DMS-S21),
400.0 g of dried 700-800 cSt STPDMS (Gelest DMS-S27), and 3.832 g
VTAS. The STPDMS had been dried by degassing it in vacuum for 20
minutes. The fluid was allowed to cure in a sealed container for 7
days at 60.degree. C. and then cooled to room temperature. Its
finished viscosity was approximately 11,400 cSt.
[0263] To 50.0 g of the partially crosslinked STPDMS was added
0.041 g of the 5% sulfuric acid dispersion from Example 63. The
mixture was stirred carefully and its viscosity monitored at
approximately 30 minute intervals. After 148 minutes, its viscosity
had increased to approximately 36,700 cSt. To this thickened fluid
was added 0.018 g of precipitated calcium carbonate powder (Solvay
Winnofil SPM). The mixture was stirred carefully to facilitate
neutralization of the sulfuric acid.
[0264] To the fluid was added 0.40 g of TMB. When stirred, this
mixture immediately thickened into a borosilicone putty. The
density of vinyl groups in this VPCB is approximately 0.033
M/kg.
Example 67
VPCB with 0.025M Vinyl Groups per Kilogram made from
Sulfuric-Acid-Treated Partially Crosslinked STPDMS
[0265] A partially crosslinked STPDMS fluid was prepared by
combining 500.0 g of dried 700-800 cSt STPDMS (Gelest DMS-S27) and
2.903 g VTAS. The STPDMS had been dried by degassing it in vacuum
for 20 minutes. The fluid was allowed to cure in a sealed container
for 7 days at 60.degree. C. and then cooled to room temperature.
Its finished viscosity was approximately 17,200 cSt.
[0266] To 50.0 g of the partially crosslinked STPDMS was added
0.041 g of the 5% sulfuric acid dispersion from Example 63. The
mixture was stirred carefully and its viscosity monitored at
approximately 30 minute intervals. After 151 minutes, its viscosity
had increased to approximately 49,200 cSt. To this thickened fluid
was added 0.015 g of precipitated calcium carbonate powder (Solvay
Winnofil SPM). The mixture was stirred carefully to facilitate
neutralization of the sulfuric acid.
[0267] To the fluid was added 0.35 g of TMB. When stirred, this
mixture immediately thickened into a borosilicone putty. The
density of vinyl groups in this VPCB is approximately 0.025
M/kg.
Example 68
VPCB made from Partially Crosslinked 90-120 cSt STPDMS Cured at
200.degree. C.
[0268] 100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to
140.degree. C. and, while stirring rapidly with a magnetic stirrer,
2.58 g VTAS was added. The mixture was further heated to about
200.degree. C. and the stirring continued. After 50 minutes, the
viscosity of the mixture was still low so an additional 0.368 g of
VTAS was added. The fluid began to gel within seconds. Before the
fluid could solidify, it was cooled quickly to room temperature and
approximately 0.165 g TMB were added to convert it to a VPCB. It
was left to dry in the open air overnight.
Example 69
VPCB made from Partially Crosslinked 90-120 cSt STPDMS Cured at
190.degree. C.
[0269] 100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21, Lot BE-12804)
was heated to 165.degree. C. and, while stirring rapidly with a
magnetic stirrer, 2.77 g VTAS was added. The mixture was further
heated to about 190.degree. C. and the stirring continued. After 60
minutes, the viscosity of the mixture began to increase noticeably.
After 80 minutes, the mixture had partially gelled. Before the
fluid could solidify, it was cooled quickly to room temperature and
approximately 0.165 g TMB were added to convert it to a VPCB. It
was left to dry in the open air overnight.
Example 70
VPCB made from Partially Crosslinked 90-120 cSt STPDMS Cured at
190.degree. C.
[0270] 100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to
150.degree. C. and, while stirring rapidly with a magnetic stirrer,
2.40 g VTAS was added. The mixture was further heated to about
190.degree. C. and the stirring continued. After 60 minutes, the
viscosity of the mixture began to increase noticeably. After 80
minutes, the mixture's viscosity had increased to the point where
the magnetic stirrer could no longer turn properly. The fluid was
cooled to room temperature and approximately 0.165 g TMB were added
to convert it to a VPCB. It was left to dry in the open air
overnight.
Example 71
VPCB made from Partially Crosslinked 700-800 cSt STPDMS Cured at
182.degree. C.
[0271] 300.0 g of 700-800 cSt STPDMS (Gelest DMS-S27) was heated to
150.degree. C. and, while stirring rapidly with a magnetic stirrer,
2.44 g VTAS was added. The mixture was further heated to about
182.degree. C. and the stirring continued. After 90 minutes, the
viscosity of the mixture began to increase noticeably. The fluid
was cooled to about 100.degree. C. and 2.3 g of TMB were added to
convert it to a VPCB. It was left to dry in the open air
overnight.
Example 72
VPCB made from Partially Crosslinked 90-120 cSt STPDMS Cured at
180.degree. C.
[0272] 400.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to
100.degree. C. and 8.848 g VTAS was added while stirring at 500 rpm
with a high-shear immersion blade. The temperature was increased
gradually to about 180.degree. C. After 170 minutes, drips of fluid
from a glass rod produced stringy tails. The vulcanizable partially
crosslinked silicone fluid was allowed to cool to room temperature
and its viscosity was measured at about 2700 cSt. When TMB was
added to a small portion of this fluid, it immediately formed a
VPCB.
Example 73
VPCB made from Partially Crosslinked 90-120 cSt STPDMS Cured at
180.degree. C.
[0273] 400.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) that had been
stored in an open container for several months was heated to
100.degree. C. and 9.585 g VTAS was added while stirring at 250 rpm
with a high-shear immersion blade. The temperature was increased
gradually to about 180.degree. C. After 220 minutes, drips of fluid
from a glass rod produced stringy tails. The vulcanizable partially
crosslinked silicone fluid was allowed to cool to room temperature
and its viscosity was measured at about 7000 cSt. When TMB was
added to a small portion of this fluid, it immediately formed a
VPCB.
Example 74
[0274] Peroxide-Cure VSR Based on 67% VPCB (4.5 wt % VTAS and 1.7
wt % TMB in 70 cSt STPDMS) and 33% high-consistency silicone rubber
(HCR) (Wacker R420/50), blended and softened with 0.5 wt % Oleic
acid, and Crosslinked using 0.57 wt % VX Peroxide
[0275] 3069.0 g of 70 cSt STPDMS (Masil SFR 70, Emerald Performance
Materials) was dried in vacuum for 5 minutes. To this fluid was
slowly added 138.1 g VTAS while stirring rapidly. The beaker
containing this mixture was heated to approximately 120.degree. C.
in a convection oven for 350 minutes and the partially crosslinked
silicone fluid was then allowed to cool. The dynamic viscosity of
this PCS at room temperature was 300 mPas.
[0276] To 50.0 g of the PCS were added 0.375 g oleic acid (0.50 wt
%) and then 0.850 g of TMB (1.7 wt %). The viscous mixture was
vacuum dried for about 5 minutes. 25.0 g of HCR silicone (Wacker
Elastosil R420/50) were added and the blend was kneaded to
homogeneity in a slip roll. It was spread as thin sheets on,Teflon
and allowed to equilibrate and dry for several hours at 70.degree.
C.
[0277] To 10.5 g of the blend were added 0.060 g VX (0.57 wt %) and
the vulcanizable material was kneaded to homogeneity in the slip
roll. It was placed in a Teflon mold and cured at 160.degree. C.
for 15 minutes. The resulting viscoelastic silicone rubber had a
Shore Hardness of 54O at t=0, 32O at t=5 sec, and 19O at t=60
sec.
Example 75
Peroxide-Cure VSR Based on 67% VPCB (3.0 wt % VTAS and 0.95 wt %
TMB in 100 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended and
Softened with 0.5 wt % Oleic Acid, and Crosslinked using 0.57 wt %
VX Peroxide
[0278] 3100.0 g of 100 cSt STPDMS (Masil SFR 100, Emerald
Performance Materials) was dried in vacuum for 5 minutes. To this
fluid was slowly added 93.0 g VTAS while stirring rapidly. The
beaker containing this mixture was heated to approximately
120.degree. C. in a convection oven for 350 minutes and the
partially crosslinked silicone fluid was then allowed to cool. The
dynamic viscosity of this PCS at room temperature was 510 mPas.
[0279] To 50.0 g of the PCS were added 0.375 g oleic acid (0.50 wt
%) and then 0.475 g of TMB (0.95 wt %). The viscous mixture was
vacuum dried for about 5 minutes. 25.0.g of HCR silicone (Wacker
Elastosil R420/50) were added and the blend was kneaded to
homogeneity in a slip roll. It was spread as thin sheets on Teflon
and allowed to equilibrate and dry for several hours at 70.degree.
C.
[0280] To 10.5 g of the blend were added 0.060 g VX (0.57 wt %) and
the vulcanizable material was kneaded to homogeneity in the slip
roll. It was placed in a Teflon mold and cured at 160.degree. C.
for 15 minutes. The resulting viscoelastic silicone rubber had a
Shore Hardness of 48O at t=0, 210 at t=5 sec, and 16O at t=60
sec.
Example 76
Peroxide-Cure VSR Based on 67% VPCB (0.7 wt % VTAS and 0.40 wt %
TMB in 750 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended and
Softened with 0.4 wt % Oleic Acid, and Crosslinked using 0.38 wt %
VX Peroxide
[0281] 1172.80 g of 750 cSt STPDMS (Masil SFR 750, Emerald
Performance Materials) was dried in vacuum for 5 minutes. To this
fluid was slowly added 8.210 g VTAS while stirring rapidly. The
beaker containing this mixture was heated to approximately
135.degree. C. in a convection oven for 300 minutes and the
partially crosslinked silicone fluid was then allowed to cool. The
dynamic viscosity of this PCS at room temperature was 7000
mPas.
[0282] To 50.0 g of the PCS were added 0.300 g oleic acid (0.40 wt
%) and then 0.200 g of TMB (0.40 wt %). The viscous mixture was
vacuum dried for about 5 minutes. 25.0 g of HCR silicone (Wacker
Elastosil R420/50) were added and the blend was kneaded to
homogeneity in a slip roll. It was spread as thin sheets on Teflon
and allowed to equilibrate and dry for several hours at 70.degree.
C.
[0283] To 10.5 g of the blend were added 0.040 g VX (0.38 wt %) and
the vulcanizable material was kneaded to homogeneity in the slip
roll. It was placed in a Teflon mold and cured at 160.degree. C.
for 15 minutes. The resulting viscoelastic silicone rubber had a
Shore Hardness of 28O at t=0, 7O at t=5 sec, and 2O at t=60
sec.
Example 77
Peroxide-Cure VSR Based on 67% VPCB (0.4 wt % VTAS and 0.35 wt %
TMB in 2000 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended and
Softened with 0.2 wt % Oleic Acid, and Crosslinked using 0.38 wt %
VX Peroxide
[0284] 1012.8 g of 2000 cSt STPDMS (Masil SFR 2000, Emerald
Performance Materials) was dried in vacuum for 5 minutes. To this
fluid was slowly added 4.051 g VTAS while stirring rapidly. The
beaker containing this mixture was heated to approximately
135.degree. C. in a convection oven for 300 minutes and the
partially crosslinked silicone fluid was then allowed to cool. The
dynamic viscosity of this PCS at room temperature was 14,500
mPas.
[0285] To 50.0 g of the PCS were added 0.150 g oleic acid (0.2 wt
%) and then 0.175 g of TMB (0.40 wt %). The viscous mixture was
vacuum dried for about 5 minutes. 25.0 g of HCR silicone (Wacker
Elastosil R420/50) were added and the blend was kneaded to
homogeneity in a slip roll. It was spread as thin sheets on Teflon
and allowed to equilibrate and dry for several hours at 70.degree.
C.
[0286] To 10.5 g of the blend were added 0.040 g VX (0.38 wt %) and
the vulcanizable material was kneaded to homogeneity in the slip
roll. It was placed in a Teflon mold and cured at 160.degree. C.
for 15 minutes. The resulting viscoelastic silicone rubber had a
Shore Hardness of 250 at t=0, 110 at t=5 sec, and 50 at t=60
sec.
* * * * *