U.S. patent application number 11/460685 was filed with the patent office on 2008-01-31 for shape memory polymer articles with a microstructured surface.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Robert K. Galkiewicz, Mieczyslaw H. Mazurek, Jeffrey M. Olofson, Audrey A. Sherman, James R. Starkey, Wendi J. Winkler, Haiyan Zhang.
Application Number | 20080027199 11/460685 |
Document ID | / |
Family ID | 38981787 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080027199 |
Kind Code |
A1 |
Mazurek; Mieczyslaw H. ; et
al. |
January 31, 2008 |
SHAPE MEMORY POLYMER ARTICLES WITH A MICROSTRUCTURED SURFACE
Abstract
A shape memory polymer article is disclosed. The article may
include a surface having a microstructure and it may include a
shape memory polymer. The shape memory polymer may include a
copolymer network. The copolymer network may be formed from the
reaction product of a free radically polymerizable siloxane having
greater than one functional free radically polymerizable group and
at least one (meth)acrylate monomer.
Inventors: |
Mazurek; Mieczyslaw H.;
(Roseville, MN) ; Galkiewicz; Robert K.;
(Roseville, MN) ; Sherman; Audrey A.; (St. Paul,
MN) ; Starkey; James R.; (Menomonie, WI) ;
Winkler; Wendi J.; (Minneapolis, MN) ; Zhang;
Haiyan; (Woodbury, MN) ; Olofson; Jeffrey M.;
(Oakdale, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
38981787 |
Appl. No.: |
11/460685 |
Filed: |
July 28, 2006 |
Current U.S.
Class: |
528/10 |
Current CPC
Class: |
A61L 24/046 20130101;
A61L 24/06 20130101; C08F 290/148 20130101; A61L 15/26 20130101;
A61L 15/26 20130101; C08F 283/12 20130101; A61L 15/24 20130101;
A61L 2400/16 20130101; A61L 15/24 20130101; A61L 24/06 20130101;
C08F 283/00 20130101; C08L 33/08 20130101; C08L 83/04 20130101;
C08L 83/04 20130101; C08L 33/08 20130101; Y10T 428/24355 20150115;
A61L 24/046 20130101; C08F 290/068 20130101 |
Class at
Publication: |
528/10 |
International
Class: |
C08G 77/00 20060101
C08G077/00 |
Claims
1. An article, comprising: a polymeric member including a surface
having a microstructure; and wherein the polymeric member comprises
a shape memory polymer, the shape memory polymer comprising a
copolymer network comprising the reaction product of a free
radically polymerizable siloxane having greater than one functional
free radically polymerizable group and at least one (meth)acrylate
monomer, wherein the at least one (meth)acrylate monomer, when
homopolymerized, forms a homopolymer having a glass transition
temperature, a melting temperature, or both greater than about
40.degree. C.
2. The article of claim 1, wherein the free radically polymerizable
siloxane has a number average molecular weight of about
1,000-200,000 grams per mole.
3. The article of claim 1, wherein the free radically polymerizable
siloxane includes a telechelic siloxane.
4. The article of claim 2, wherein the telechelic siloxane includes
(meth)acryloxyurea siloxane.
5. The article of claim 2, wherein the telechelic siloxane includes
acrylamidoamido siloxane.
6. The article of claim 2, wherein the telechelic siloxane includes
methacrylamidoamido siloxane.
7. The article of claim 2, wherein the telechelic siloxane includes
methylstyrylurea siloxane.
8. The article of claim 1, wherein the (meth)acrylate monomer
includes isobornyl acrylate.
9. The article of claim 1, wherein the copolymer network includes
about 10-70 weight-percent of the free radically polymerizable
siloxane.
10. The article of claim 1, wherein the copolymer network includes
about 10-60 weight-percent of the free radically polymerizable
siloxane.
11. The article of claim 1, wherein the copolymer network includes
about 20-60 weight-percent of the free radically polymerizable
siloxane.
12. The article of claim 1, wherein the polymeric member includes a
secondary surface having a microstructure.
13. An article, comprising: a polymeric member including a
microstructured surface, wherein the microstructured surface
includes a surface feature that is not visible to an unaided eye;
and wherein the polymeric member includes a shape memory
polymer.
14. The article of claim 13, wherein the shape memory polymer
comprises a copolymer network comprising the reaction product of a
free radically polymerizable siloxane having greater than one
functional free radically polymerizable group and at least one
(meth)acrylate monomer, wherein the at least one (meth)acrylate
monomer, when homopolymerized, forms a homopolymer having a glass
transition temperature, a melting temperature, or both greater than
about 40.degree. C.
15. The article of claim 14, wherein the free radically
polymerizable siloxane has a number average molecular weight of
about 1,000-200,000 grams per mole.
16. The article of claim 14, wherein the (meth)acrylate monomer
includes isobornyl acrylate.
17. The article of claim 14, wherein the free radically
polymerizable siloxane includes a telechelic siloxane.
18. The article of claim 17, wherein the telechelic siloxane
includes (meth)acryloxyurea siloxane, acrylamidoamido siloxane,
methacrylamidoamido siloxane, or methylstyrylurea siloxane.
19. The article of claim 13, wherein the surface feature includes a
plurality of depressions.
20. The article of claim 13, wherein the surface feature includes a
plurality of projections.
21. The article of claim 13, wherein the polymeric member includes
a secondary surface having a microstructure.
22. An article, comprising: a polymeric member including a
microstructured surface, wherein the microstructured surface
includes a surface feature that is not visible to an unaided eye;
and wherein the polymeric member includes a shape memory polymer,
the shape memory polymer comprising a copolymer network comprising
the reaction product of (meth)acryloxyurea siloxane and isobornyl
acrylate.
23. An article comprising a shape memory polymer having a
microstructured surface and comprising a copolymer network, the
copolymer network comprising the reaction product of a free
radically polymerizable siloxane having greater than one functional
free radically polymerizable group and at least one (meth)acrylate
monomer, wherein the at least one (meth)acrylate monomer, when
homopolymerized, forms a homopolymer having a glass transition
temperature greater than about 40.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to commonly assigned, co-pending
U.S. patent application Ser. No. ______ by Sherman et al., entitled
"Method of Forming and Using Shape Memory Polymer," and filed of
even date herewith (Docket 62183US002); and to commonly assigned,
co-pending U.S. patent application Ser. No. ______ by Dunn et al.,
entitled "Microlens Sheeting With Floating Image Using A Shape
Memory Material," and filed of even date herewith (Docket
62252US002).
FIELD OF THE INVENTION
[0002] The invention relates to shape memory polymers, and
particularly, to shape memory polymers having microstructured
surfaces.
BACKGROUND
[0003] Shape memory materials have the unique ability to "remember"
a pre-set shape and, upon exposure to the appropriate stimuli,
shift from a deformed or altered shape back to the pre-set shape.
Several commercially important uses have been developed for shape
memory materials. For example, shape memory metal alloys are
commonly used in various medical, dental, mechanical, and other
technology areas for a wide variety of products.
[0004] Shape memory polymers and the uses of these materials have
emerged more recently. However, the basic premise behind these
materials is the same--that the material can be pre-set in a
particular shape, deformed, and then revert back to the pre-set
shape when exposed to the appropriate stimuli.
SUMMARY
[0005] The present disclosure relates generally to shape memory
polymer articles. The shape memory polymer articles may include a
microstructured surface.
[0006] In one embodiment, an illustrative article is described that
includes a polymeric member. The polymeric member may include a
surface having a microstructure and it may include a shape memory
polymer. The shape memory polymer may include a copolymer network.
The copolymer network may include the reaction product of a free
radically polymerizable siloxane having greater than one functional
free radically polymerizable group and at least one (meth)acrylate
monomer. The at least one (meth)acrylate monomer, when
homopolymerized, may form a homopolymer that has a glass transition
temperature, a melting temperature, or both greater than about
40.degree. C.
[0007] In another embodiment, an illustrative article is described
that includes a polymeric member having a microstructured surface.
The microstructured surface may include a surface feature that is
not visible to an unaided eye. The polymeric member may include a
shape memory polymer.
[0008] In yet another embodiment, an illustrative article is
described that includes a polymeric member having a microstructured
surface. The microstructured surface may include a surface feature
that is not visible to an unaided eye. The polymeric member may
include a shape memory polymer. The shape memory polymer may
include a copolymer network. The copolymer network may include the
reaction product of (meth)acryloxyurea siloxane and isobornyl
acrylate.
[0009] The above summary of the present invention is not intended
to describe each disclosed embodiment or every implementation of
the present invention. The Figures, Detailed Description and
Examples, which follow, more particularly exemplify these
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0011] FIG. 1 is a side view of an illustrative article having a
surface with a microstructure;
[0012] FIG. 2 is a side view of another illustrative article having
a surface with a microstructure; and
[0013] FIG. 3 is an alternative side view of the illustrative
article shown in FIG. 2.
[0014] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0015] Generally, this disclosure is directed to shape memory
polymer articles that have a microstructured surface. While the
present invention is not so limited, an appreciation of various
aspects of the invention will be gained through discussion of the
various features and components provided below.
Selected Definitions
[0016] All numeric values are herein assumed to be modified by the
term "about," whether or not explicitly indicated. The term "about"
generally refers to a range of numbers that one of skill in the art
would consider equivalent to the recited value (i.e., having the
same function or result). In many instances, the terms "about" may
include numbers that are rounded to the nearest significant
figure.
[0017] Weight percent, percent by weight, wt %, wt-%, % by weight,
and the like are synonyms that refer to the concentration of a
substance as the weight of that substance divided by the weight of
the composition and multiplied by 100.
[0018] The recitation of numerical ranges by endpoints includes all
numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2,
2.75, 3, 3.80, 4, and 5).
[0019] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents unless
the content clearly dictates otherwise. As used in this
specification and the appended claims, the term "or" is generally
employed in its sense including "and/or" unless the content clearly
dictates otherwise.
[0020] As used herein, the term "alkyl" refers to a straight or
branched chain monovalent hydrocarbon radical optionally containing
one or more heteroatomic substitutions independently selected from
S, O, Si, or N. Alkyl groups generally include those with one to
twenty atoms. Alkyl groups may be unsubstituted or substituted with
those substituents that do not interfere with the specified
function of the composition. Substituents include alkoxy, hydroxy,
mercapto, amino, alkyl substituted amino, or halo, for example.
Examples of "alkyl" as used herein include, but are not limited to,
methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, and
isopropyl, and the like.
[0021] As used herein, the term "aryl" refers to monovalent
unsaturated aromatic carbocyclic radicals having a single ring,
such as phenyl, or multiple condensed rings, such as naphthyl or
anthryl. Aryl groups may be unsubstituted or substituted with those
substituents that do not interfere with the specified function of
the composition. Substituents include alkoxy, hydroxy, mercapto,
amino, alkyl substituted amino, or halo, for example. Such an aryl
ring may be optionally fused to one or more of another heterocyclic
ring(s), heteroaryl ring(s), aryl ring(s), cycloalkenyl ring(s), or
cycloalkyl rings. Examples of "aryl" as used herein include, but
are not limited to, phenyl, 2-naphthyl, 1-naphthyl, biphenyl,
2-hydroxyphenyl, 2-aminophenyl, 2-methoxyphenyl and the like.
[0022] As used herein the term (meth)acrylate is used to define
both acrylates and methacrylates.
[0023] The term telechelic siloxane refers to siloxanes with 2
reactive groups, one at either end of the siloxane chain.
[0024] As used herein, the term shape memory polymer refers to
polymeric materials that are stimuli-responsive. Upon application
of an external stimuli they have the ability to change their shape.
A change in shape initiated by a change in temperature can be
referred to as a thermally induced shape memory effect. While not
being bound by theory, the shape memory effect may result from the
polymer's structure, that is, its morphology in combination with a
certain processing and programming technology. Therefore, the
shape-memory behavior can be observed for several polymers that may
differ significantly in their chemical composition.
Articles
[0025] The present disclosure is directed to articles. The articles
may include a polymeric member that has a surface with a
microstructure and that includes a shape memory polymer. The
articles contemplated span a vast array of technical fields and
include essentially any structure that may find utility or
otherwise benefit from having a shape memory polymer incorporated
into their construction. This may include a variety of different
devices, apparatuses, components or portions of devices, layers or
surfaces on devices, and the like, or any other suitable structure.
For example, the articles of this disclosure may include an
adhesive, a tape or substrate including an adhesive, a
heat-activated tape, a microstructured tape, a backing member, a
foam tape, a device having a fluid disposed or encapsulated
therein, a microfluidic device, a circuit or circuit board, a
printed circuit, a film (including multilayer optical films), a
micromachined article, an embossed article, a printing plate or
film used to create 3D prints, a substrate for pattern coating
and/or pattern printing, an electrode, a device having cube corners
with retroreflective characteristics, a secure identification
article, a secure license or license plate, a directional organic
light emitting diode, a sensor, an indicator, a switch, and the
like, or any other suitable device. It should be noted that this
list of articles is not intended to be limiting as the articles
contemplated can take the form of any suitable structure,
apparatus, or device.
[0026] As indicated above, an exemplary article may include a shape
memory polymer. Some examples of shape memory polymers suitable for
the articles are described in more detail below. In some
embodiments, the entire article is made from the shape memory
polymer. In other embodiments, only a portion of the article is
made from a shape memory polymer. This may include a shape memory
polymer layer, a shape memory polymer surface, a shape memory
polymer portion, or any other suitable configuration. When only a
portion of the article is made from a shape memory polymer, the
remaining materials making up the article may include metals, metal
alloys, polymers, ceramics, and the like, or any other suitable
material. Regardless of whether the article is completely or
partially made from a shape memory polymer, the articles described
herein can be described as "shape memory polymer articles".
[0027] Shape memory polymers are known to have the unique ability
to be set in a pre-set shape, deformed to an altered shape, and
then revert back to the pre-set shape when exposed to the
appropriate stimuli (e.g., changes in temperature, application of
solvent, etc.). Because the articles disclosed herein include a
shape memory polymer, the portion of the article (or all of the
article if made completely from a shape memory polymer) having the
shape memory polymer can be configured to utilize this property.
For example, the article may include a shape memory polymer surface
that has been cast or otherwise shaped to have a pre-set shape or
configuration. This surface can be deformed to an altered or
deformed shape and then be shifted back to the pre-set shape when
appropriately cued. Triggering the shift from the deformed shape to
the pre-set shape can vary depending on the particular polymer used
or other parameters. However, at least some of the shape memory
polymers disclosed herein can be shifted by exposure to elevated
temperatures and/or to an appropriate solvent.
[0028] Also as indicated above, the articles include a surface
having a microstructure. Generally, a surface with a microstructure
is different than a "flat" or unstructured surface. As used herein,
the term "microstructure" means the configuration of features
wherein at least 2 dimensions of the features are microscopic. The
topical and/or cross-sectional view of the features, therefore, are
microscopic. As used herein, the term "microscopic" refers to
features of small enough dimension so as to require an optic aid to
the naked eye when viewed from any plane of view to determine its
shape. One criterion is found in Modern Optic Engineering by W. J.
Smith, McGraw-Hill, 1966, pages 104-105 whereby visual acuity," . .
. is defined and measured in terms of the angular size of the
smallest character that can be recognized." Normal visual acuity is
considered to be when the smallest recognizable letter subtends an
angular height of 5 minutes of arc on the retina. At a typical
working distance of 250 mm (10 inches), this yields a lateral
dimension of 0.36 mm (0.0145 inch) for this object.
[0029] The microstructures may be formed along portions or all of
any number of surfaces of the article. For example, some surfaces
of the articles may include sections that have microstructures and
sections that are free from microstructures. Alternatively,
substantially all of one or more surfaces of the articles may
include microstructures. In addition, the shape and/or
configuration of the microstructures can also vary. For example,
microstructures can include one or more projections, one or more
depressions, a combination of projections and depressions, ridges,
posts, pyramids, hemispheres, cones, protrusion, or any other
suitable feature. The shapes of the various projections and/or
depressions can also vary. For example, some embodiments of
projections and/or depressions can be rounded in shape (e.g.,
circular, semicircular, spherical, hemispherical, oval,
pill-shaped, partially pill-shaped, etc.) or include a rounded
portion, polygonal in shape or include a polygonal portion (e.g.,
triangular, squared, cubed including cube corners, tetrahedrical,
rectangular, paralleopiped, pentagonal, hexagonal, etc.), an
irregular shape, a regular shape, a pointed shape, a truncated
shape, combinations thereof, or any other suitable shape. In at
least some of these as well as in other embodiments, the
projections and/or depressions may include or define one or more
channels, valleys, wells, ridges, and the like, combinations
thereof, or any other configuration.
[0030] Microstructures may be formed in a surface of an article
through the use of a microstructured molding tool. A
microstructured molding tool is an implement for imparting a
structure or finish to at least a portion of an article and that
may be continuously reused in the process. Microstructured molding
tools can be in the form of a planar stamping press, a flexible or
inflexible belt, a roller, or the like. Furthermore,
microstructured molding tools are generally considered to be tools
from which the microstructured surface feature is generated by
embossing, coating, casting, or platen pressing and do not become
part of the finished microstructured article. Instead, a surface on
the article corresponding to where the article came into contact
with the microstructured surface of the molding tool defines the
microstructure or microstructured surface feature of the
article.
[0031] A broad range of methods are known to those skilled in this
art for generating microstructured molding tools. Examples of these
methods include but are not limited to photolithography, etching,
discharge machining, ion milling, micromachining, and
electroforming. Microstructured molding tools can also be prepared
by replicating various microstructured surfaces, including
irregular shapes and patterns, with a moldable material such as
those selected from the group consisting of crosslinkable liquid
silicone rubber, radiation curable urethanes, etc. or replicating
various microstructures by electroforming to generate a negative or
positive replica intermediate or final embossing tool mold. Also,
microstructured molds having random and irregular shapes and
patterns can be generated by chemical etching, sandblasting, shot
peening or sinking discrete structured particles in a moldable
material. Additionally any of the microstructured molding tools can
be altered or modified according to the procedure taught in U.S.
Pat. No. 5,122,902, the entire disclosure of which is herein
incorporated by reference.
[0032] For illustration purposes, FIG. 1 is provided to depict a
portion of an example article 10. Article 10 includes a shape
memory polymer such as, for example, any of the shape memory
polymers described herein. Article 10 may comprise a polymeric
member that includes a surface 12 having a plurality of surface
features or microstructures 14 formed therein. In this example,
microstructures 14 are depicted as projections extending outward
from surface 12. However, this arrangement is not intended to be
limiting as a wide variety of differing arrangements are
contemplated including those described above.
[0033] Depending on the application, article 10 may be in the
"pre-set" shape or may be in the "deformed" shape. If article 10,
as shown in FIG. 1, is in the pre-set shape, surface 12 can be
deformed. This may be accomplished, for example, by changing the
configuration of microstructures 14. For example, microstructures
14 may be flattened. The deformed article 10 can be shifted back to
the pre-set configuration (i.e., the configuration depicted in FIG.
1 for this example) upon exposure to, for example, increased
temperature, solvent, or any other suitable stimuli. Alternatively,
if article 10 is in the deformed shape or configuration when
arranged as shown in FIG. 1, exposure to the appropriate stimuli
may shift article 10 back to the pre-set shape. In this later
embodiment, the pre-set shape may include a generally flat or
planar arrangement for surface 12 or any other suitable shape.
[0034] FIGS. 2-3 depict another example article 1010. Article 1010
may comprise, a sensor. In this embodiment, article 1010 may
include a surface 1012 having a microstructure defined therein. The
microstructure may include, for example, a plurality of rows or
wells 1014. This configuration may be the pre-set shape of surface
1012. Surface 1012 can be deformed into a deformed shape that is,
for example, substantially flat. A secondary surface 1012', for
example on the opposite side of article 1010 (which is indicated in
FIG. 3 as article 1010') may have a generally flat pre-set shape
that can be deformed to have a microstructure that includes or
defines a hexagonal pattern therein. Mobilizing may restore both
surfaces 1012/1012'. For example, surface 1012 may shift back to
the pre-set shape (see FIG. 2) and opposite surface 1012' may shift
back to a substantially flat shape. In this embodiment, mobilizing
may include the application of heat and/or the exposure to solvent
or solvent vapors to one or both of surface 1012 and/or surface
1012'. For example, surfaces 1012/1012' may be exposed to heat and
restored. Alternatively, surfaces 1012/1012' may be exposed to
solvent or solvent vapors. This later embodiment may allow article
1010 to be used as a sensor that can "smell" a solvent. For
example, a user may visually observe the changes in the shape of
article 1010 (on one or both sides) in order to observe that the
sensor has smelled a particular solvent.
[0035] FIGS. 2-3, in addition to illustrating that article 1010 can
be used as a sensor, also indicate that a surface having a pre-set
shape may be formed on multiple sides of an article. For example,
FIGS. 2-3 illustrate article 1010 having surface 1012 with a
pre-set shape that includes a microstructure whereas surface 1012'
has a pre-set shape that is generally planar. In these embodiments
or embodiments of the same spirit, one or both of the surfaces
1012/1012' can be deformed. For example, surface 1012 can be
flattened whereas surface 1012' can be deformed to have a
microstructure. Thus, article 1010 can be seen as having a
secondary surface 1012' with a microstructure. It can be
appreciated that secondary surface 1012' may, alternatively, have a
pre-set shape that includes the microstructure shown in FIG. 3 and
it can be deformed to have another shape. Moreover, the secondary
surface 1012' (or other surfaces having a pre-set shape) may be
defined along any area of the article 1010 and need not be limited
to just a surface that is opposite of surface 1012. Regardless of
the configuration of surfaces 1012/1012', mobilization shifts
surfaces 1012/1012' back to their pre-set shape. It can be
appreciated that other articles are contemplated that have multiple
surfaces with pre-set shapes including multiple planar surfaces
and/or multiple surfaces with microstructures. Moreover, other
embodiments are contemplated where one or more surfaces have a
microstructure formed therein and one or more of these surfaces can
be deformed to have a different microstructure.
Shape Memory Polymers
[0036] As described above, the articles disclosed herein include a
shape memory polymer. Shape memory polymers can be classified as
elastomers. On the molecular level they represent polymer networks
that include segment chains that are connected by netpoints. The
netpoints can be formed by entanglements of the polymer chains or
intermolecular interaction of certain polymer blocks. These
cross-links are called physical netpoints. Cross-links in the form
of covalent bonds form chemical netpoints. An elastomer exhibits a
shape-memory functionality if the material can be stabilized in the
deformed state in a temperature range that is relevant for the
particular application. This can be achieved by using the network
chains as a kind of molecular switch. For this purpose, it should
be possible to limit the flexibility of the segments as a function
of temperature. This process is supposed to be reversible. The
ability to incorporate a control function into the material
provides a thermal transition T.sub.trans of the network chains in
the temperature range of interest for the particular application.
At temperatures above T.sub.trans the chain segments are flexible,
whereas the flexibility of the chains below this thermal transition
is at least partially limited. In the case of a transition from the
rubber-elastic, i.e., viscous, to the glassy state the flexibility
of the entire segment is limited.
[0037] Without being bound to theory, it is believed that the
copolymer network includes an elastomeric phase or component and a
"glassy" or high glass transition temperature phase or component.
The glassy phase holds or constrains the elastomeric component so
that the substrate can be deformed into and stays in the deformed
shape. Shifting from a deformed shape to the pre-set shape
generally includes mobilizing the glassy phase of the shape memory
polymer in order to allow the elastomeric component to "spring
back" or otherwise shift to the original pre-set shape. According
to this theory, mobilizing is understood to be the mobilization of
the glassy phase through the application of the appropriate
external stimuli.
[0038] In at least some embodiments, the elastomeric phase
comprises a free radically polymerizable siloxane having greater
than one functional free radically polymerizable group. The glassy
phase may comprise at least one (meth)acrylate monomer that, when
homopolymerized, forms a homopolymer having a glass transition
temperature, a melting temperature, or both greater than about
40.degree. C. According to these embodiments, exposure of the shape
memory polymer to temperatures greater than 40.degree. C. can
mobilize the glassy phase and cause the deformed surface of the
substrate from the deformed shape to the pre-set shape. In other
embodiments, a solvent such as alkyl alcohol, acetone, etc. can
partially dissolve or plasticize the glassy phase and effectuate
the same change. In some embodiments, the (meth)acrylate monomer
may crystallize when reacted with the free radically polymerizable
siloxane having greater than one functional free radically
polymerizable group. In these embodiments, exposing the copolymer
network to temperatures above the melting point of the
(meth)acrylate monomer may mobilize the glassy phase.
[0039] The relative proportions of the various components of the
copolymer network can vary. For example, in at least some
embodiments, the copolymer network may include about 10-70
weight-percent of the free radically polymerizable siloxane. In
other embodiments, the copolymer network may include about 10-60
weight-percent of the free radically polymerizable siloxane. In
still other embodiments, the copolymer network may include about
20-60 weight-percent of the free radically polymerizable
siloxane.
Free Radically Polymerizable Siloxanes
[0040] The free radically polymerizable siloxanes for use in the
copolymer networks may be represented by the following formula:
##STR00001##
wherein:
[0041] X is a group having ethylenic unsaturation;
[0042] Y is a divalent linking group;
[0043] m is an integer of 0 to 1;
[0044] D is selected from the group consisting of hydrogen, an
alkyl group of 1 to about 10 carbon atoms, aryl, and substituted
aryl;
[0045] R is a divalent hydrocarbon group;
[0046] R.sub.1 are monovalent moieties which can be the same or
different selected from the group consisting of alkyl, substituted
alkyl, aryl, and substituted aryl;
[0047] R.sub.2 are monovalent moieties which can be the same or
different selected from the group consisting of alkyl, substituted
alkyl, aryl, and substituted aryl;
[0048] R.sub.3 are monovalent moieties which can be the same or
different selected from the group consisting of alkyl, substituted
alkyl, vinyl, aryl, and substituted aryl;
[0049] R.sub.4 are monovalent moieties which can be the same or
different selected from the group consisting of alkyl, substituted
alkyl, vinyl, aryl, and substituted aryl; and
[0050] n is an integer of about 10 to about 2000.
[0051] Some examples of suitable free radically polymerizable
siloxanes for use in the articles described herein may include
those described in U.S. Pat. No. 5,091,483, the entire disclosure
of which is herein incorporated by reference.
[0052] In at least some embodiments, the free radically
polymerizable siloxanes comprise telechelic siloxanes. The
telechelic siloxanes may include, for example, (meth)acryloxyurea
siloxane (MAUS), acrylamidoamido siloxane (ACMAS),
methacrylamidoamido siloxane (MACMAS), and methylstyrylurea
siloxane (MeStUS). In general, these telechelic siloxanes are
formed by reacting silicone diamines with capping reagents such as
isocyanatoethylmethacrylate (IEM), vinyldimethylazlactone (VDM),
isopropenyl dimethyl azlactone (IDM), and m-isopropenyl alpha,
alpha-dimethyl benzyl isocyanate (m-TMI), respectively. These
telechelic siloxanes may have a number average molecular weights in
the range of about 1,000 to 200,000. Some additional details
regarding synthesis is provided below. Particularly preferred
telechelic siloxanes are those that include a polydimethylsiloxane
chain and may also be referred to as polydimethylsiloxanes.
[0053] The telechelic siloxanes have free radically polymerizable
end groups. Due to the polar nature of the hydrogen bonding end
groups and the nonpolar nature of the polydimethylsiloxane chain, a
transient network is formed wherein the polar end groups tend to
associate with each other. The relative strength of the end group
association for the various telechelic siloxanes is reflected in
their viscosities, with higher viscosities seen in the case of the
more strongly associating end groups (e.g., ACMAS and MeStUS).
[0054] Functional polymers, like these telechelic siloxanes, that
are easy to cure to elastomers are often referred to as "liquid
rubbers." Indeed, by the exposure of telechelic siloxanes having
free radically polymerizable end groups to low-intensity UV
radiation (when the system contains photoinitiator), silicone
elastomers with controlled properties can be obtained.
[0055] In general the telechelic siloxanes are obtained from
amine-functional siloxane intermediates. Suitable
polydiorganosiloxane diamines and methods of making the
polydiorganosiloxane diamines are described, for example, in U.S.
Pat. No. 3,890,269 (Martin), U.S. Pat. No. 4,661,577 (Jo Lane et
al.), U.S. Pat. No. 5,026,890 (Webb et al.), U.S. Pat. No.
5,276,122 (Aoki et al.), U.S. Pat. No. 5,214,119 (Leir et al.),
U.S. Pat. No. 5,461,134 (Leir et al.), U.S. Pat. No. 5,512,650
(Leir et al.), and U.S. Pat. No. 6,355,759 (Sherman et al.),
incorporated herein by reference in their entirety. Some
polydiorganosiloxane diamines are commercially available, for
example, from Shin Etsu Silicones of America, Inc., Torrance,
Calif. and from Gelest Inc., Morrisville, Pa. Particularly useful
polydiorganosiloxane diamines include
bis(3-aminopropyl)polydimethylsiloxanes.
[0056] Polydimethylsiloxanes having acrylamidoamido end groups
(ACMAS) can be prepared by the reaction of a polydimethylsiloxane
diamine with 2 equivalents of vinyl dimethyl azlactone (VDM).
Similarly, polydimethylsiloxanes having methacrylamidoamido end
groups (MACMAS) can be prepared in the same manner by the reaction
of a polydimethylsiloxane diamine with 2 equivalents of isopropenyl
dimethyl azlactone (IDM).
[0057] Polydimethylsiloxanes having methacryloxyurea end groups
(MAUS) can be prepared using the same procedure, by the reaction of
a polydimethylsiloxane with 2 equivalents of isocyanatoethyl
methacrylate (IEM).
[0058] Polydimethylsiloxanes having alpha-methylstyrylurea end
groups (MeStUS) can be made by the reaction of a
polydimethylsiloxane with 2 equivalents of
m-isopropenyl-alpha,alpha-dimethyl benzyl isocyanate (m-TMI).
[0059] In other embodiments the free radically polymerizable
siloxanes comprise non-techelic siloxanes. These siloxanes are ones
according to the above formula where at least some of the groups
R.sub.3 and/or R.sub.4 comprise vinyl groups.
(Meth)Acrylate Monomers
[0060] Generally, (meth)acrylate monomers are monomers that are the
(meth)acrylate esters of non-tertiary alkyl alcohols, the alkyl
groups of which comprise from about 1 to about 20, or about 1 to
about 18 carbon atoms. Suitable (meth)acrylate monomers include,
for example, benzyl methacrylate, cyclohexyl acrylate, cyclohexyl
methacrylate, ethyl methacrylate, isobornyl acrylate, isobornyl
methacrylate, methyl methacrylate, 1-methylcyclohexyl methacrylate,
2-methylcyclohexyl methacrylate, 3-methylcyclohexyl methacrylate,
4-methylcyclohexyl methacrylate, and 2-phenoxy ethyl
methacrylate.
[0061] Particularly suitable (meth)acrylate monomers are those
that, when homopolymerized, form a homopolymer having a glass
transition temperature, a melting temperature, or both greater than
about 40.degree. C. These monomers are suitable in forming a
copolymer network with a free radically polymerizable siloxane.
Examples of preferred (meth)acrylate monomers include isobornyl
acrylate, cyclohexyl acrylate, trimethyl cyclohexyl acrylate,
methyl methacrylate, methacrylic acid, t-butyl acrylate. A single
(meth)acrylate monomer or a combination of (meth)acrylate monomers
may be used.
[0062] The glass transition temperature (and/or the melting
temperature) may be measured by conventional techniques such as
Differential Scanning Calorimetry (DSC) or Dynamic Mechanical
Analysis (DMA). Some additional details regarding these components
of the copolymer network are described in more detail below.
Curing Initiator
[0063] As indicated above, the shape memory polymer may be a
copolymer network including the reaction product of a free
radically polymerizable siloxane having greater than one functional
free radically polymerizable group and at least one (meth)acrylate
monomer. The reaction may include, for example, polymerization via
curing. Curing may be carried out in an oxygen-free, e.g., in an
inert atmosphere such as nitrogen gas or by utilizing a barrier of
radiation-transparent material having low oxygen permeability.
Curing can also be carried out under an inerting fluid such as
water. When visible or ultraviolet radiation is used for curing,
the reaction may also contain a photoinitiator. Suitable
photoinitiators include benzoin ethers, benzophenone and
derivatives thereof, acetophenone derivatives, camphorquinone, and
the like. Some examples of commercially available photoinititaors
include DARACUR 1173, DAROCUR 4265, IRGACURE 651, IRGACURE 1800,
IRGACURE 369, IRGACURE 1700, and IRGACURE 907, commercially from
Ciba Geigy. The photoinitiator may be used at a concentration of
from about 0.1% to about 5% by weight of the total polymerizable
composition, and, if curing is carried out under an inerting fluid,
the fluid is preferably saturated with the photoinitiator or
photoinitiators being utilized in order to avoid the leaching of
initiator from the reaction. The rapid cure observed for these
materials allows for the use of relatively low levels of
photoinitiator, hence uniform cure of thick sections can be
achieved due to deeper penetration of radiation. If desired, curing
can also be achieved thermally, which may include the use of
thermal initiator such as peroxides, azo compounds, or persulfates
generally at a concentration of from about 1% to about 5% by weight
of the total polymerizable composition. In at least some
embodiments, any initiator (thermal or photo-) utilized may be
soluble in the reaction components themselves, thereby avoiding the
need for a separate solvent. Liquid initiators may be
preferred.
Preparation of Silicone-Acrylate Copolymeric Networks
[0064] Polymerization mixtures can be prepared by dissolving
telechelic siloxanes in the (meth)acrylate monomers and adding a
photoinitiator Such polymerization mixtures typically have
viscosities that permit the preparation of samples in film form by
direct coating and radiation curing by standard procedures.
[0065] The shape memory polymer article may be formed by coating
and curing the polymerizable mixture in a structured configuration,
by curing the polymerization mixture in an unstructured
configuration and then applying a structure through the imposition
of heat and pressure, or by a combination of the these
processes.
[0066] For example, the polymerization mixture can be coated onto a
carrier layer such as a liner (either structured or unstructured),
onto a substrate (such as a metal sheet or foil, a film, a ceramic
or piece of glass, etc) or onto a tool or mold. The coated
polymerization mixture is then covered with a covering layer which
may be another liner, substrate, tool or mold and may be the same
or different from the carrier layer. The resulting construction is
then cured, preferably with UV radiation. Upon curing one or both
of the carrier layer and or the covering layer are removed and the
shape memory polymer article may then be subjected to additional
processing (to create or remove structuring, to form in articles of
a desired shape, etc).
[0067] The entire disclosures of the following patents, which are
referred to in the various Examples, are herein incorporated by
reference: U.S. Pat. No. 5,514,730, U.S. Pat. No. 5,706,132, and
U.S. Pat. No. 6,569,521.
EXAMPLES
[0068] These examples are merely for illustrative purposes only and
are not meant to be limiting on the scope of the appended claims.
All parts, percentages, ratios, etc. in the examples and the rest
of the specification are by weight, unless noted otherwise.
Solvents and other reagents used were obtained from Sigma-Aldrich
Chemical Company; Milwaukee, Wis. unless otherwise noted.
TABLE-US-00001 Table of Abbreviations Abbreviation or Trade
Designation Description 5K MAUS Methacryloxyurea siloxane, a
difunctional silicone acrylate prepared from PDMS diamine 5K as
described in U.S. Pat. No. 5,514,730 column 14 for 35K MAUS, using
5,000 g/mole PDMS diamine instead of 35,000 g/mole PDMS diamine.
PDMS Polydimethyl siloxane DAROCUR Photoinitiator:
2-hydroxy-2-methyl-1-phenyl-propan-1-one from Ciba 1173 Specialty
Chemicals, Hawthorne, NY. PET Unprimed polyester film of
polyethylene terephthalate having a thickness of 50 or 125
micrometers. 5K MeStUS Alpha-methyl styrylurea siloxane, a
difunctional silicone alpha-methyl styrene prepared from PDMS
diamine 5K as described in U.S. Pat. No. 5,514,730 column 14 for
35K MeStUS, using 5,000 g/mole PDMS diamine instead of 35,000
g/mole PDMS diamine. 5K ACMAS Acrylamidoamido siloxane, a
difunctional silicone acrylamido prepared from PDMS diamine 5K as
described in U.S. Pat. No. 5,514,730 column 14 for 35K ACMAS, using
5,000 g/mole PDMS diamine instead of 35,000 g/mole PDMS diamine.
50K MAUS Methacryloxyurea siloxane, a difunctional silicone
acrylate prepared from PDMS diamine 50K as described in U.S. Pat.
No. 5,514,730 column 14 for 35K MAUS, using 50,000 g/mole PDMS
diamine instead of 35,000 g/mole PDMS diamine. 50K MeStUS
Alpha-methyl styrylurea siloxane, a difunctional silicone
alpha-methyl styrene prepared from PDMS diamine 50K as described in
U.S. Pat. No. 5,514,730 column 14 for 35K MeStUS, using 50,000
g/mole PDMS diamine instead of 35,000 g/mole PDMS diamine. 50K
ACMAS Acrylamidoamido siloxane, a difunctional silicone acrylamido
prepared from PDMS diamine 50K as described in U.S. Pat. No.
5,514,730 column 14 for 35K ACMAS, using 50,000 g/mole PDMS diamine
instead of 35,000 g/mole PDMS diamine. Water-borne Acrylate polymer
dispersion at 40% solids. PSA
Example 1
[0069] A curable precursor solution of 40 parts of 5K MAUS
dissolved in 60 parts of IBA, containing 0.5 wt % DAROCUR 1173 was
poured on the first tool, which was an unstructured PET film laid
down on the surface of a glass plate. The first tool was bordered
by a compliant adhesive film of 3 millimeters thickness to serve as
a dam for the curable adhesive precursor as well as a spacer to
control the thickness of the cured film. The liquid layer of
curable precursor was covered with a cover sheet (an unstructured
UV transparent film) and the excess fluid was squeezed out by
placing a rigid glass plate over the cover sheet and pressing the
thus formed sandwich construction until the glass plate rested
against the spacer. The sandwich construction was exposed to low
intensity UV lights through the cover sheet for 10-15 minutes. The
resulting cured film (slab) had two surfaces replicated from the
first tool and from the cover sheet (second tool) and was removed
from both the first tool and from the cover sheet. The edges of the
substrate were trimmed.
Example 2
[0070] The slab prepared in Example 1 was deformed by pressing
against the structured surface of the metal tool and a polished
steel plate with heat/pressure (110.degree. C. for 10 minutes,
pre-press 4.1 MegaPascals (600 lbs/in.sup.2) for 10 minutes, 30
MegaPascals (2 ton/in.sup.2) high pressure for 10 minutes) and
quenched (25 minutes until temperature reached 60.degree. C.). The
structure of the tool--an array of tilted triangular prisms with
millimeter-size dimensions, was partially replicated--approximately
60-70% of the height of the pyramid.
Example 3
[0071] A part of the film made in Example 2 was heated to
approximately 110.degree. C. on a heating plate. The area exposed
to heat became essentially flat, with some traces of the embossed
microstructure still visible.
Example 4
[0072] A shape-memory substrate was prepared as described in
Example 2. One part of the sample was submitted to a secondary
process of shaving off the temporary surface features. When the
sample was heated to 120.degree. C. the portion of the sample with
shaved-off material showed rounded cavities with topologies
corresponding to the shaved-off elements.
Example 5
[0073] A shape-memory substrate was prepared as described in
Example 1 except that the first tool was a microstructured film
having linear array of rectangular channels (200 micrometers at the
bottom, 100 micrometers at the top, 200 micrometer high) and a 1
millimeter spacer was used. The sample was flattened between the
two polished steel plates under the conditions as described in
Example 2 except flat tools were used. One part of the film was
sprayed with metallic silver paint to form a thin layer of metallic
silver. The electrical conductivity of the sample was checked using
a Fluke 87 III RMS Multimeter, which was independent of the
position of the electrodes (x and y conductive). A portion of the
sample was heated to 120.degree. C. on a heating plate to restore
the original shape of the surface. Electrical conductivity of the
sample was again checked. While the sample maintained the
electrical conductivity along the channels the conductivity in the
cross-direction was primarily destroyed and/or disrupted.
Example 6
[0074] A shape-memory substrate was made as described in Example 1
except that the first tool was a metal tool with structured
surfaces as described in Example 2. The substrate having sharp
macroscopic features was subsequently submitted to heat and
pressure between two polished steel plates under the conditions
described in Example 2 except flat tools were used. The substrate
became essentially flat with the pyramids being partially flattened
and partially bent. Part of the original structure was restored by
selectively focusing sunlight through a lens onto several of the
pyramids.
Example 7
[0075] A shape-memory substrate was tested through the stages of
making, distorting and restoring. The sample was made as described
in Example 1 except that the first tool was a metal tool having an
array of cube corners as described in U.S. Pat. No. 5,706,132. The
pyramids had a height of 87 micrometers (3.5 mil). The spacer used
was 125 micrometers. The sample was removed from the first tool
while maintained on the flat PET cover. The sample showed
retroreflectivity when analyzed using a retroviewer (the sample
"made" stage). A part of the sample was flattened between the two
polished steel plates under the conditions described in Example 2
except that the tools were flat. It was noticed that the height of
the pyramids were reduced, but the pyramidal shape of the flattened
microfeatures was maintained (the sample "distorted" stage). The
sample showed no retroreflectivity in a retroviewer. A portion of
the sample was heated to 120.degree. C., which restored the
original shape of the pyramids and the retroreflectivity of the
sample (the sample "restored" stage).
Example 8-13
[0076] A series of samples were made, distorted and restored as in
Example 7 except that different compositions of the curable
precursors were used (containing Monomer 1, IBA and DAROCUR 1173)
as shown in Table 1. Results of the testing are shown in Table
2.
TABLE-US-00002 TABLE 1 Monomer 1 Monomer 1 IBA DAROCUR 1173 Example
Identity (parts) (parts) (wt %) 8 5K MeStUS 50 50 0.5 9 5K MAUS 50
50 0.5 10 5K ACMAS 50 50 0.5 11 50K MeStUS 50 50 0.5 12 50K MAUS 50
50 0.5 13 50K ACMAS 50 50 0.5
TABLE-US-00003 TABLE 2 Appearance Sample Appearance As After
Appearance Example Color Made Distortion Distortion As Restored 8
Clear Retroreflective Flattened to No retroreflection
Retroreflective Cubes 0.6 Cubes micrometers 9 Clear Retroreflective
Flattened to No retroreflection Retroreflective Cubes 1.0 Cubes
micrometers 10 Bluish Retroreflective Flattened to No
retroreflection Retroreflective Haze Cubes 2.0 Cubes micrometers 11
Clear Retroreflective Flattened to No retroreflection
Retroreflective Cubes 1.0 Cubes micrometers 12 Clear
Retroreflective Flattened to No retroreflection Retroreflective
Cubes 1.5 Cubes micrometers 13 Clear Retroreflective Flattened to
No retroreflection Retroreflective Cubes 7.8 Cubes micrometers
Example 14
[0077] A shape-memory substrate was made as described in Example 1
except that a 125 micrometers spacer was used. One of the surfaces
of the substrate was deformed by pressing the sample between the
metal tool, having regularly arranged square posts (150 micrometers
at the bottom, 150 micrometers at the top, 50 micrometers high), to
create a corresponding array of microcavities. The substrate was
coated with a Water-borne PSA. Upon drying the water at 25.degree.
C. for 24 hours, the film contained PSA distributed within the
pockets of microstructure substrate and showed no/little tack. A
portion of the sample was heated to 120.degree. C. on a heating
plate causing the restoration of the original flatness of the
substrate and making the sample tacky by exposing the PSA layer on
the surface.
Example 15
[0078] A shape-memory substrate was made as described in Example 1
except that a 1 millimeter spacer was used. One of the surfaces of
the substrate was deformed by pressing the sample between the metal
tool, having an array of triangular posts (420 micrometers depth),
to create an array of visible cavities. The substrate was flooded
with colored aqueous fluid to fill the cavities. Silicone pressure
sensitive adhesive tape (as described in U.S. Pat. No. 6,569,521,
Example 28) was laminated to the substrate to seal off the cavities
filled with the fluid. When heated to 120.degree. C. the substrate
returned to its original shape exerting pressure on the laminated
tape causing the tape to also distort, and causing the adhesive
border seals to rupture.
Example 16
[0079] A shape-memory substrate was made as described in Example 1,
except that the first tool was a metal tool, a replica of the tool
used to deform the substrate in Example 14, having regularly
arranged square cavities (150 micron at the bottom, 150 micron at
the top, 45 micrometer high) and a 1 millimeter spacer to create a
corresponding array of micro-posts. The sample was flattened
between two polished steel plates under the conditions as described
in Example 2. The sample was heated to 120.degree. C. on a heating
plate to restore the original structure (posts) of the surface. The
posts were able to pick up water-based ink for transfer to
paper.
Example 17
[0080] A shape-memory substrate was made as described in Example 1
except that a 125 micrometers spacer was used. One of the surfaces
of the substrate was deformed by pressing the sample between the
metal tool having regularly arranged square posts, as described in
Example 14, to create a corresponding array of micro-cavities. When
a droplet of the solution of dye (bromothymol blue, sodium salt) in
ethylene glycol was deposited on the surface of the film, clear-cut
borders along the line of the pattern were naturally established,
and the solvent essentially restored the "printed" area to flatness
with the clearly visible high concentration of the dye in the spots
corresponding to the arrangement of cavities in which it was
originally deposited.
Example 18
[0081] A shape-memory substrate was made as described in Example 1
except that a 125 micrometers spacer was used and the first tool
was a metal tool with an array of square posts, as described in
Example 14. The cured sample was pressed between 2 flat surfaces
using the technique described in Example 2. When a droplet of the
solution of dye (bromothymol blue, sodium salt) in ethylene glycol
was deposited on the surface of the film, clear-cut borders along
the line of the pattern were naturally established, and the solvent
essentially restored the "printed" area to its micro-cavitated form
dragging the ink into the cavities.
Examples 19
[0082] A shape-memory substrate was made as described in Example 1
except that a 125 micrometers spacer was used. One of the surfaces
of the cured substrate was deformed by pressing the sample between
the metal tool, used in Example 16. A droplet of the aqueous
solution of dye (bromophenol blue indicator solution) was deposited
and pressed on the microstructured surface of the shape-memory
substrate. The solution was primarily distributed in the channels
between the posts, and on the top of the posts having some small
micro-channels. When exposed to heat (120.degree. C.), the solvent
(water) evaporated and the flatness of the first surface of the
substrate was essentially restored leaving a regular pattern of the
dye on the surface.
Example 20
[0083] A shape-memory substrate was made as described in Example 1
except that a 125 micrometers spacer was used. One of the surfaces
of the substrate was deformed by pressing the sample between the
metal tool (an array of cube corners as described in U.S. Pat. No.
5,706,132, pyramidal height of 87 micrometers), as described in
Example 2. A border of adhesive was made on a plastic substrate and
the microstructured surface was placed within and on the border.
The retroreflectivity of the microstructured surface disappeared
where in contact with the adhesive border, but remained
retroreflective within the border.
[0084] The present invention should not be considered limited to
the particular examples described above, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention may be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the instant specification.
* * * * *