U.S. patent application number 10/617582 was filed with the patent office on 2005-01-13 for epoxy-capped polythioethers.
This patent application is currently assigned to PRC-DeSoto International, Inc.. Invention is credited to Rao, Chandra Bhushan, Sawant, Suresh.
Application Number | 20050010003 10/617582 |
Document ID | / |
Family ID | 33565004 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050010003 |
Kind Code |
A1 |
Sawant, Suresh ; et
al. |
January 13, 2005 |
Epoxy-capped polythioethers
Abstract
Epoxy-capped polythioethers and curable compositions of
epoxy-capped polythioethers are disclosed.
Inventors: |
Sawant, Suresh; (Stevenson
Ranch, CA) ; Rao, Chandra Bhushan; (Valencia,
CA) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Assignee: |
PRC-DeSoto International,
Inc.
Glendale
CA
|
Family ID: |
33565004 |
Appl. No.: |
10/617582 |
Filed: |
July 11, 2003 |
Current U.S.
Class: |
525/523 |
Current CPC
Class: |
C07D 303/22 20130101;
C08L 63/00 20130101; C08G 59/302 20130101 |
Class at
Publication: |
525/523 |
International
Class: |
C08G 059/02 |
Claims
What is claimed is:
1. An epoxy-capped polythioether having the following structural
formula: 7wherein R.sup.1 is selected from the group consisting of
C.sub.2-6 n-alkylene, C.sub.3-6 branched alkylene, C.sub.6-8
cycloalkylene, C.sub.6-10 alkylcycloalkylene, and
--[--(CHR.sup.3).sub.p--X--].sub.q--CH- R.sup.3).sub.r--, wherein
each R.sup.3 is independently selected from H, and --CH.sub.3 each
X is independently selected from O, S, --NH--, and --NR.sup.4--,
R.sup.4 is selected from H, and --CH.sub.3, p is an integer from 2
to 6, q is an integer from 1 to 5, and r is an integer from 2 to
10, and each R.sup.2 is a divalent linking group.
2. The epoxy-capped polythioether of claim 1, wherein R.sup.1 is
derived from a compound selected from the group consisting of
dimercaptodioxaoctane, and dimercaptodiethylsulfide.
3. The epoxy-capped polythioether of claim 1, wherein each R.sup.2
is derived from an olefin.
4. The epoxy-capped polythioether of claim 3, wherein the olefin is
selected from the group consisting of an alkylene having from 3 to
20 carbon atoms, and an oxyalkylene having from 3 to 20 carbon
atoms.
5. The epoxy-capped polythioether of claim 3, wherein the olefin is
selected from the group consisting of an alkylene having from 3 to
5 carbon atoms, and an oxyalkylene having from 3 to 5 carbon
atoms.
6. The epoxy-capped polythioether of claim 1, wherein each R.sup.2
is derived from a compound selected from the group consisting of
allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-7-octene,
1,2-epoxy-9-decene, 4-vinyl-1-cyclohexene 1,2-epoxide, butadiene
monoepoxide, isoprene monoepoxide, and limonene monoepoxide.
7. The epoxy-capped polythioether of claim 1, which is free of
hydrolysable chlorine.
8. An epoxy-capped polythioether having the following structural
formula: 8where R.sup.1 and R.sup.2 have the meanings set forth in
claim 1, B is a multivalent radical, and z is a number
corresponding to the valence of B.
9. The epoxy-capped polythioether of claim 8, wherein each R.sup.1
is independently derived from a compound selected from the group
consisting of dimercaptodioxaoctane, and
dimercaptodiethylsulfide.
10. The epoxy-capped polythioether of claim 8, wherein each R.sup.2
is derived from an olefin.
11. The epoxy-capped polythioether of claim 10, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 20 carbon atoms, and an oxyalkylene having from 3 to 20 carbon
atoms.
12. The epoxy-capped polythioether of claim 10, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 5 carbon atoms, and an oxyalkylene having from 3 to 5 carbon
atoms.
13. The epoxy-capped polythioether of claim 8, wherein each R.sup.2
is derived from a compound selected from the group consisting of
allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-7-octene,
1,2-epoxy-9-decene, 4-vinyl-1-cyclohexene 1,2-epoxide, butadiene
monoepoxide, isoprene monoepoxide, and limonene monoepoxide.
14. The epoxy-capped polythioether of claim 8, which is free of
hydrolysable chlorine.
15. The epoxy-capped polythioether of claim 8, wherein z is from 3
to 6.
16. The epoxy-capped polythioether of claim 8, having an average
functionality between 2.05 and 3.
17. The epoxy-capped polythioether of claim 8, wherein B is derived
from a compound selected from the group consisting of a polyacid, a
polyamine, a polyanhydride, and a polythiol.
18. A curable composition comprising: (a) at least one epoxy-capped
polythioether of claim 1; and (b) at least one curing agent.
19. The curable composition of claim 18, wherein the at least one
curing agent is selected from the group consisting of a polyacid, a
polyamine, a polyanhydride, and a polythiol.
20. The curable composition of claim 18, further comprising at
least one adjuvant resin different from (a) and (b).
21. The curable composition of claim 18, further comprising at
least one filler.
22. The curable composition of claim 18, further comprising at
least one additive selected from the following: plasticizers,
pigments, cure accelerators, adhesion promoters, thixotropic
agents, fire retardants, masking agents, antioxidants, and
surfactants.
23. The curable composition of claim 18, which is free of
hydrolysable chlorine.
24. A curable composition comprising: (a) at least one epoxy-capped
polythioether of claim 8; and (b) at least one curing agent.
25. The curable composition of claim 24, wherein the at least one
curing agent is selected from the group consisting of a polyacid, a
polyamine, a polyanhydride, and a polythiol.
26. The curable composition of claim 24, further comprising at
least one adjuvant resin different from (a) and (b).
27. The curable composition of claim 24, further comprising at
least one filler.
28. The curable composition of claim 24, further comprising at
least one additive selected from the following: plasticizers,
pigments, cure accelerators, adhesion promoters, thixotropic
agents, fire retardants, masking agents, antioxidants, and
surfactants.
29. The curable composition of claim 24, which is free of
hydrolysable chlorine.
30. An epoxy-capped polythioether formed by reacting n moles of a
compound having the structure of Formula I, HS--R.sup.1--SH I
wherein R.sup.1 is selected from the group consisting of C.sub.2-6
n-alkylene, C.sub.3-6 branched alkylene, C.sub.6-8 cycloalkylene,
C.sub.6-10 alkylcycloalkylene, and
--[--(CHR.sup.3).sub.p--X--].sub.q--(CHR.sup.3).s- ub.r--, wherein
R.sup.3 is selected from H, and --CH.sup.3, each X is independently
selected from O, S, --NH--, and --NR.sup.4--, R.sup.4 is selected
from H, and --CH.sub.3, p is an integer from 2 to 6, q is an
integer from 1 to 5, and r is an integer from 2 to 10, or a mixture
of at least two different compounds having the structure of Formula
I, with n+1 moles of a compound having the structure of Formula II:
9wherein R.sup.2 forms a divalent linking group, or a mixture of at
least two different compounds having the structure of Formula
II.
31. The epoxy-capped polythioether of claim 30, wherein R.sup.1 is
derived from a compound selected from the group consisting of
dimercaptodioxaoctane, and dimercaptodiethylsulfide.
32. The epoxy-capped polythioether of claim 30, wherein each
R.sup.2 comprises an olefin.
33. The epoxy-capped polythioether of claim 32, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 20 carbon atoms, and an oxyalkylene having from 3 to 20 carbon
atoms.
34. The epoxy-capped polythioether of claim 32, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 5 carbon atoms, and an oxyalkylene having from 3 to 5 carbon
atoms.
35. The epoxy-capped polythioether of claim 30, wherein each
R.sup.2 is derived from a compound selected from the group
consisting of allyl glycidyl ether, 1,2-epoxy-5-hexene,
1,2-epoxy-7-octene, 1,2-epoxy-9-decene, 4-vinyl-1-cyclohexene
1,2-epoxide, butadiene monoepoxide, isoprene monoepoxide, and
limonene monoepoxide.
36. The epoxy-capped polythioether of claim 30, which is free of
hydrolysable chlorine.
37. The epoxy-capped polythioether of claim 30, having an epoxy
equivalent weight range less than 300.
38. The epoxy-capped polythioether of claim 30, having an epoxy
equivalent weight range less than 150.
39. The epoxy-capped polythioether of claim 30, which is formed in
the presence of a catalyst selected from the group consisting of a
free-radical catalyst, an ionic catalyst, and ultraviolet
light.
40. The epoxy-capped polythioether of claim 39, wherein the
catalyst does not comprise an acidic or basic compound and does not
produce acidic or basic compounds upon decomposition.
41. The epoxy-capped polythioether of claim 39, wherein the
catalyst comprises a free-radical catalyst.
42. The epoxy-capped polythioether of claim 41, wherein the
free-radical catalyst is selected from the group consisting of
azo-type catalysts, and alkylperoxides.
43. An epoxy-capped polythioether formed by reacting a compound
having the structure of Formula I, HS--R.sup.1--SH I wherein
R.sup.1 is selected from the group consisting of C.sub.2-6
n-alkylene, C.sub.3-6 branched alkylene, C.sub.6-8 cycloalkylene,
C.sub.6-10 alkylcycloalkylene, and
--[--(CHR.sup.3).sub.p--X--].sub.q--CHR.sup.3).sub.r--, wherein
R.sup.3 is selected from H, and --CH.sub.3, each X is independently
selected from O, S, --NH--, and --NR.sup.4--, R.sup.4 is selected
from H, and --CH.sub.3, p is an integer from 2 to 6, q is an
integer from 1 to 5, and r is an integer from 2 to 10, or a mixture
of at least two different compounds having the structure of Formula
I, with a compound having the structure of Formula II: 10wherein
R.sup.2 forms a divalent linking group, or a mixture of at least
two different compounds having the structure of Formula II, and
with a polyfunctionalizing agent, or a mixture of at least two
different polyfunctionalizing agents.
44. The epoxy-capped polythioether of claim 43, having an average
functionality between 2.05 and 3.
45. The epoxy-capped polythioether of claim 43, wherein the
polyfunctionalizing agent has a valence of 3.
46. The epoxy-capped polythioether of claim 43, wherein the
functionality of the polyfunctionalizing agent is selected from the
group consisting of acid groups, amine groups, anhydride groups,
and thiol groups.
47. The epoxy-capped polythioether of claim 43, wherein the
polyfunctionalizing agent is selected from the group consisting of
a polyacid, a polyamine, a polyanhydride, a polythiol, and mixtures
thereof.
48. The epoxy-capped polythioether of claim 43, wherein each
R.sup.2 comprises an olefin.
49. The epoxy-capped polythioether of claim 48, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 20 carbon atoms, and an oxyalkylene having from 3 to 20 carbon
atoms.
50. The epoxy-capped polythioether of claim 48, wherein the olefin
is selected from the group consisting of an alkylene having from 3
to 5 carbon atoms, and an oxyalkylene having from 3 to 5 carbon
atoms.
51. The epoxy-capped polythioether of claim 43, wherein each
R.sup.2 is derived from a compound selected from the group
consisting of allyl glycidyl ether, 1,2-epoxy-5-hexene,
1,2-epoxy-7-octene, 1,2-epoxy-9-decene, 4-vinyl-1-cyclohexene
1,2-epoxide, butadiene monoepoxide, isoprene monoepoxide, and
limonene monoepoxide.
52. The epoxy-capped polythioether of claim 43, which is free of
hydrolysable chlorine.
53. The epoxy-capped polythioether of claim 43, having an epoxy
equivalent weight range less than 300.
54. The epoxy-capped polythioether of claim 43, having an epoxy
equivalent weight range less than 150.
55. The epoxy-capped polythioether of claim 43, which is formed in
the presence of a catalyst selected from the group consisting of a
free-radical catalyst, an ionic catalyst, and ultraviolet
light.
56. The epoxy-capped polythioether of claim 55, wherein the
catalyst does not comprise an acidic or basic compound and does not
produce acidic or basic compounds upon decomposition.
57. The epoxy-capped polythioether of claim 55, wherein the
catalyst comprises a free-radical catalyst.
58. The epoxy-capped polythioether of claim 57, wherein the
free-radical catalyst is selected from the group consisting of
azo-type catalysts, and alkylperoxides.
Description
FIELD OF THE INVENTION
[0001] This invention generally relates to epoxy-capped
polythioethers and curable compositions of epoxy-capped
polythioethers.
BACKGROUND OF INVENTION
[0002] It is desirable that sealants, coatings, and adhesives used
in aviation and aerospace applications exhibit flexibility, fuel
resistance, and high-temperature resistance. In general, these
properties may be accomplished by incorporating polythioether
linkages into the backbone of polymer resins.
[0003] Flexible, fuel resistant epoxy-terminated polysulfides have
been developed which exhibit good fuel resistance. These compounds
are typically formed using epichlorohydrin as a reactant.
Epichlorohydrin is extremely toxic and the synthesis of
epoxy-terminated polysulfides using epichlorohydrin generates
corrosive hydrolysable chlorine ("HYC") as an undesirable
byproduct. Further, the compounds formed using epichlorohydrin
incorporate un-reacted epichlorohydrin that must be removed by
thorough washing. Such epoxy-terminated polysulfides typically
exhibit a relatively high viscosity of about 30 poise at 25.degree.
C. and a broad epoxy equivalent weight range.
[0004] There is a need for improved flexible, fuel resistant, and
high-temperature resistant epoxy-capped polythioethers and
compositions of epoxy-capped polythioethers synthesized by methods
that are environmentally compatible and that do not produce toxic
byproducts. Further, it is desirable to produce epoxy-capped
polythioethers with a controlled and narrow epoxy equivalent weight
range.
[0005] The epoxy-capped polythioethers of the invention formed by
the addition of thiol across the double bond of a monoepoxide
comprising an olefinic group are flexible, fuel resistant and the
high-conversion synthesis does not generate hydrolysable chlorine
and avoids the use of epichlorohydrin. The epoxy capped
polythioethers of the invention exhibit a controlled and narrow
epoxy-equivalent weight distribution.
SUMMARY OF THE INVENTION
[0006] To address the limitations of known epoxides for aviation
and aerospace application there is provided epoxy-capped
polythioethers and curable compositions of epoxy-capped
polythioethers.
[0007] One aspect of the invention provides epoxy-capped
polythioethers having the structure of Formula I: 1
[0008] wherein
[0009] R.sup.1 is selected from the group consisting of C.sub.2-6
n-alkylene, C.sub.3-6 branched alkylene, C.sub.6-8 cycloalkylene,
C.sub.6-10 alkylcycloalkylene,
--[--CHR.sup.3).sub.p--X--].sub.q(CHR.sup.- 3).sub.r--,
[0010] wherein
[0011] each R.sup.3 is independently selected from H, and
CH.sub.3,
[0012] each X is independently selected from O, S, --NH--, and
--NR.sup.4--,
[0013] R.sup.4 is selected from H, and --CH.sub.3,
[0014] p is an integer from 2 to 6,
[0015] q is an integer from 1 to 5, and
[0016] r is an integer from 2 to 10,
[0017] and each R.sup.2 is a divalent linking group.
[0018] A second aspect of the invention provides epoxy-capped
polythioethers formed by reacting n moles of a compound having the
structure of Formula II wherein R.sup.1 has the meaning described
above:
HS--R.sup.1--SH II
[0019] with n+1 moles of a compound having the structure of Formula
III wherein R.sup.2 forms a divalent linking group: 2
[0020] A third aspect of the invention provides curable
compositions of the epoxy-capped polythioethers of the
invention.
[0021] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
DETAILED DESCRIPTION
[0022] Unless otherwise indicated, all numbers expressing
quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being
modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in
the following specification and attached claims are approximations
that may vary depending upon the desired properties to be obtained
by the present invention. At the very least, and not as an attempt
to limit the application of the doctrine of equivalents to the
scope of the claims, each numerical parameter should at least be
construed in light of the number of reported significant digits and
by applying ordinary rounding techniques.
[0023] Consistent with the invention, one embodiment provides
epoxy-capped polythioethers having the structure of Formula I:
3
[0024] wherein
[0025] R.sup.1 is selected from the group consisting of C.sub.2-6
n-alkylene, C.sub.3-6 branched alkylene, C.sub.6-8 cycloalkylene,
C.sub.6-10 alkylcycloalkylene,
--[--CHR.sup.3).sub.p--X--].sub.q--CHR.sup- .3).sub.r--,
[0026] wherein
[0027] each R.sup.3 is independently selected from H, and
CH.sub.3,
[0028] each X is independently selected from O, S, --NH--, and
--NR.sup.4--,
[0029] R.sup.4 is selected from H, and --CH.sub.3,
[0030] p is an integer from 2 to 6,
[0031] q is an integer from 1 to 5, and
[0032] r is an integer from 2 to 10,
[0033] and each R.sup.2 is a divalent linking group, typically
alkylene or oxyalkylene containing from 3 to 20 carbon atoms.
[0034] R.sup.1 is typically derived from compounds, monomers, or
polymers having at least two thiol groups. In certain embodiments,
polythiols include dithiols having the structure of Formula II:
HS--R.sup.1--SH II
[0035] where R.sup.1 can be a C.sub.2-6 n-alkylene group; a
C.sub.3-6 branched alkylene group having one or more pendent groups
which can be, for example, hydroxyl groups, and alkyl groups such
as methyl or ethyl groups; an alkyleneoxy group; a C.sub.6-8
cycloalkylene group; a C.sub.6-10 alkylcycloalkylene group; or a
--[(--CHR.sup.3).sub.p--X--].su- b.q --CHR.sup.3).sub.r-- group, p
is an independently selected integer ranging from 2 to 6, q is an
independently selected integer ranging from 1 to 5, and r is an
independently selected integer ranging from 2 to 10, and R.sup.3 is
hydrogen or methyl.
[0036] In other embodiments, dithiols may include one or more
heteroatom substituents in the carbon backbone, that is, dithiols
in which X includes a heteroatom such as O, S, or other bivalent
heteroatom radical; a secondary or tertiary amine group, i.e.,
--NR.sup.4--, where R.sup.4 may be hydrogen or methyl; or other
substituted trivalent heteroatom. In certain embodiments, X may be
O or S, and thus R.sup.1 is
--[(--CHR.sup.3).sub.p--O--].sub.q--(--CHR.sup.3).sub.r--, or
--[(CHR.sup.3).sub.p--S--].sub.q--(--CHR.sup.3).sub.r--. In certain
embodiments, p and r are equal. In certain embodiments, both p and
r have the value of 2.
[0037] In certain embodiments, the dithiols may include
dimercaptodiethylsulfide (DMDS) (p=2, r=2, q=1, X=S),
dimercaptodioxaoctane (DMDO) (p=2, q=2, r=1, X=0), and
1,5-dimercapto-3-oxapentane (p=2, r=2, q=1, X=0). In certain
embodiments, the dithiols may include both heteroatom substituents
in the carbon backbone and pendent alkyl groups, such as pendent
methyl groups. Examples of dithiols having both heteroatom
substituents in the carbon backbone and pendent alkyl groups
include methyl-substituted DMDS such as
HS--CH.sub.2CH(CH.sub.3)--S--CH.sub.2CH.sub.2--SH, and
HS--CH(CH.sub.3)CH.sub.2--S--CH.sub.2CH.sub.2--SH, and
dimethyl-substituted DMDS such as
HS--CH.sub.2CH(CH.sub.3)S--CH(CH.sub.3)- CH.sub.2--SH and
HS--CH(CH.sub.3)CH.sub.2--S--CH.sub.2CH(CH.sub.3)--SH.
[0038] In certain embodiments of epoxy-capped polythioethers having
the structure of Formula I, R.sup.1 may be a C.sub.2-6 n-alkylene
group, for example, 1,2-ethylenedithiol, 1,3-propylenedithiol,
1,4-butylenedithiol, 1,5-pentylenedithiol, or 1,6-hexylenedithiol.
In other embodiments, R.sup.1 may be a C.sub.3-6 branched alkylene
group having one or more pendent groups, for example,
1,2-propylenedithiol, 1,3-butylenedithiol, 2,3-butylenedithiol,
1,3-pentylenedithiol, and 1,3-dithio-3-methylbutylen- e. In other
embodiments, R.sup.1 may be a C.sub.6-8 cycloalkylene or C.sub.6-10
alkylcycloalkylene group, for example, dipentylenedimercaptan, and
ethylcyclohexylenedithiol (ECHDT).
[0039] Polythiols having the structure of Formula II may be
prepared by reacting, for example, a divinyl ether or mixture of
divinyl ethers with an excess of a dithiol or a mixture of
dithiols. In certain embodiments, n+1 moles of a polythiol having
the structure of Formula II or a mixture of at least two polythiols
having the structure of Formula II are reacted with n moles of a
polyvinyl ether having the structure of Formula IV:
CH.sub.2.dbd.CH--O--[R.sup.5--O--].sub.m--CH.dbd.CH.sub.2 IV
[0040] where R.sup.5 includes a C.sub.2-6 n-alkylene group, a
C.sub.3-6 branched alkylene group, a C.sub.6-8 cycloalkylene group,
a C.sub.6-10 alkylcycloalkylene group, and a
--[--(CHR.sup.3).sub.p--X--].sub.q--(CHR.- sup.3).sub.r--, group
where X, R.sup.3, p, q, and r may be as set forth above, and m can
be a rational number from 1 to 10.
[0041] Polyvinyl ethers can comprise compounds having at least one
alkyleneoxy group, and preferably from 1 to 4 alkyleneoxy groups,
such as compounds in which m is an integer from 1 to 4. In other
embodiments, m is an integer from 2 to 4. In certain embodiments,
the polyvinyl ethers comprise polyvinyl ether mixtures. Such
mixtures are characterized by a non-integral average value of the
number of alkyleneoxy groups per molecule. Thus, m in Formula IV
can also take on rational number values between 0 and 10.0, in
other embodiments between 1.0 and 10.0, in still other embodiments
between 1.0 and 4.0, and in still other embodiments between 2.0 and
4.0.
[0042] Polyvinyl ether monomers can comprise divinyl ether
monomers, such as divinyl ether, ethylene glycol divinyl ether
(EG-DVE), butanediol divinyl ether (BD-DVE), hexanediol divinyl
ether (HD-DVE), diethylene glycol divinyl ether (DEG-DVE),
triethylene glycol divinyl ether, tetraethylene glycol divinyl
ether, and polytetrahydrofuryl divinyl ether; trivinyl ether
monomers such as trimethylolpropane trivinyl ether; tetrafunctional
vinyl ether monomers such as pentaerythritol tetravinyl ether; and
mixtures thereof. In certain embodiments, the polyvinyl ether
monomer can further comprise one or more pendent groups selected
from alkylene groups, hydroxyl groups, alkeneoxy groups, and amine
groups.
[0043] Polythiols having the structure of Formula II may be
prepared by reacting compounds having olefinic groups, such as
vinylcyclohexene.
[0044] In certain embodiments, polyvinyl ethers in which R.sup.5 is
a C.sub.2-6 branched alkylene can be prepared by reacting a
polyhydroxy compound with acetylene. Exemplary compounds of this
type comprise compounds in which R.sup.5 is an alkyl-substituted
methylene group such as --CH(CH.sub.3)--, for example, PLURIOL.RTM.
blends such as PLURIOL.RTM.E-200 divinyl ether (BASF Corp.) for
which R.sup.5=ethylene and m=3.8, or an alkyl-substituted ethylene,
such as --CH.sub.2CH(CH.sub.3)--, for example, DPE.RTM. polymeric
blends including DPE.RTM.-2 and DPE.RTM.-3 (International Specialty
Products).
[0045] The reaction between a dithiol and a polyvinyl ether to
prepare a polythiol having the structure of Formula II is described
in U.S. Pat. No. 5,912,319.
[0046] The reaction between a dithiol and a polyvinyl ether to
prepare a polythiol having the structure of Formula II may take
place in the presence of a catalyst. The catalyst may be a
free-radical catalyst, an ionic catalyst, or ultraviolet radiation.
Preferably, the catalyst does not comprise acidic or basic
compounds, and does not produce acidic or basic compounds upon
decomposition. Examples of free-radical catalysts are an azo-type
catalyst, including Vazo.RTM.-57 (Du Pont), Vazo.RTM.-64 (Du Pont),
Vazo.RTM.-67 (Du Pont), V-70.RTM. (Wako Specialty Chemicals), and
V-65B.RTM. (Wako Specialty Chemicals). Examples of other
free-radical catalysts are alkyl peroxides, such as t-butyl
peroxide.
[0047] R is a divalent linking group. In certain embodiments,
R.sup.2 may be derived from a monoepoxide having the structure of
Formula III: 4
[0048] in which R.sup.2 includes groups that are reactive with
sulfides such as, for example, olefinic groups. The olefinic group
may be an alkylene group or an oxyalkylene group having from 3 to
20 carbon atoms and preferably from 3 to 5 carbon atoms. In certain
embodiments, the monoepoxides having the structure of Formula III
include allyl glycidyl ether, 1,2-epoxy-5-hexene,
1,2-epoxy-7-octene, 1,2-epoxy-9-decene, 4-vinyl-1-cyclohexene
1,2-epoxide, butadiene monoepoxide, isoprene monoepoxide, and
limonene monoepoxide.
[0049] Consistent with the invention, another embodiment provides
epoxy-capped polythioethers having the structure of Formula V:
5
[0050] where R.sup.1 and R.sup.2 are as described above, B is a
multivalent radical, and z is a number corresponding to the valence
of B.
[0051] B is a z-valent group and is derived from a compound, B',
that represents a polyfunctionalizing agent. A polyfunctionalizing
agent refers to a compound having more than two moieties that are
reactive with epoxy groups. In certain embodiments, the
polyfunctionalizing agent comprises from 3 to 6 such reactive
moieties. Typically, B is denoted as a "z-valent"
polyfunctionalizing agent, where z is the number of reactive
moieties, and hence the number of separate branches comprising the
polyfunctional epoxy-capped polythioether.
[0052] In certain embodiments of epoxy-capped polythioethers having
the structure of Formula V, the polyfunctionalizing agent is a
trifunctionalizing agent wherein z=3. In certain embodiments of a
material of Formula V, the functional groups of the
polyfunctionalizing agent are selected from acid groups, amine
groups, anhydride groups, and thiol groups. Polyfunctionalizing
agents having mixed functionality can also be used. Examples of
polyfunctionalizing agents include tricarboxylic acids such as
trimellitic acid and tricarballylic acid; polythiols such as
described in U.S. Pat. No. 4,366,307, U.S. Pat. No. 4,609,762, and
U.S. Pat. No. 5,225,472; and, triamines such as diethylene triamine
and triethylene tetraamine.
[0053] Mixtures of polyfunctionalizing agents having a range of
functionalities may also be used in the preparation of epoxy-capped
polythioethers having the structure of Formula V. In certain
embodiments, the use of certain amounts of trifunctionalizing
agents affords epoxy-capped polythioethers having average
functionalities from 2.05 to 3.0. Other average functionalities can
be achieved by using tetrafunctional polyfunctionalizing agents, or
polyfunctionalizing agents with higher valencies. The average
functionality of the resulting epoxy-capped polythioether will also
be affected by factors such as stoichiometry, as is known to those
skilled in the art.
[0054] The difunctional epoxy-capped polythioethers of the
invention having the structure of Formula I can be formed by the
reaction of n moles of a dithiol having the structure of Formula II
with n+1 moles of a monoepoxide having the structure of Formula
III. The dithiol and monoepoxide may be reacted at a temperature of
from about 40.degree. C. to about 100.degree. C., and typically
from about 60.degree. C. to 80.degree. C. The dithiol and
monoepoxide may be reacted for from about 10 hours to about 36
hours, and typically from about 12 hours to 24 hours. The dithiol
may be any compound, polymer, or monomer having at least two thiol
groups, and includes any of the exemplary polythiol compounds
previously described. In certain embodiments, the monoepoxide
having the structure of Formula II comprises one epoxy group and
one olefinic group. The monoepoxide may be any of the exemplary
monoepoxides previously described.
[0055] Optionally, the reaction occurs in the presence of a
catalyst. Examples include free-radical catalysts, ionic catalysts,
and ultraviolet light. In certain embodiments, the catalyst does
not comprise an acidic or basic compound, and does not produce
acidic or basic compounds upon decomposition. Preferably, the
catalyst may be a free-radical catalyst, such as those described
above.
[0056] Consistent with another embodiment of the invention,
polyfunctional epoxy-capped polythioethers having the structure of
Formula V can be formed by reacting at least one polythiol, at
least one polyepoxide, and at least one polyfunctionalizing agent
in appropriate stoichiometric amounts. Examples of polythiols,
polyepoxides, and polyfunctionalizing agents include those as
described above. Optionally, the reaction occurs in the presence of
a catalyst as described above.
[0057] The epoxy-capped polythioethers described above can be
combined with curing agents to form curable compositions. The
epoxy-capped polythioethers described above can also be combined
with other resins and curing agents to form curable compositions.
In certain embodiments, curable compositions of the invention
include from 0.2% to 10% by weight of at least one epoxy-capped
polythioether as described above, at least one curing agent, and at
least one resin where the weight percent is based on the total
weight of the curable composition.
[0058] The term curing agent refers to a material that reacts with
the epoxy group of the epoxy-capped polythioethers to form
crosslinks. Examples of curing agents include polyacid curing
agents, polyamine curing agents, polyanhydride curing agents, and
polythiol curing agents. A polyacid curing agent refers to a
compound having two or more acid groups per molecule which are
reactive with the epoxy-capped polythioether to form a crosslinked
composition. The acid functionality can be a carboxylic acid, or a
sulfonic acid. Preferably, the polyacid curing agent may be a
carboxyl-terminated compound having at least two carboxyl groups
per molecule. Examples of polyacid curing agents include carboxylic
acid group-containing polymers such as acrylic polymers,
polyesters, and polyurethanes; and oligomers such as ester
group-containing oligomers and monomers.
[0059] Examples of carboxylic acid-containing acrylic polymers are
copolymers of (a) an ethylenically unsaturated monomer containing
at least one carboxylic acid, and (b) a different ethylenically
unsaturated monomer that is free from carboxylic acid groups. In
certain embodiments, the amounts of monomer (a) and monomer (b) are
selected such that the acid number of the polyacid acrylic polymer
is from 30 to 150, preferably from 60 to 120. Examples of
carboxylic acid-containing acrylic monomers are acrylic acid,
methacrylic acid, maleic acid, and partial esters of maleic acid.
The other monomeric component (b) is characterized by the group,
6
[0060] and may be styrene, an alpha-substituted lower alkyl styrene
such as alpha-methylstyrene, an alkyl ester of acrylic and
methacrylic acid, such as methyl methacrylate, methyl acrylate, and
ethyl acrylate, and mixtures of these materials.
[0061] In other embodiments, the polyacid curing agent may be a
monomeric polycarboxylic acid having from 5 to 20 carbon atoms
including open chain, cyclic, saturated, unsaturated, and aromatic
acids. Examples of suitable monomeric polycarboxylic acids include
succinic acid, adipic acid, azelaic acid, sebacic acid,
hexahydrophthalic acid, maleic acid, cyclohexene-1,2-dicarboxylic
acid, and phthalic acid.
[0062] Polyamine curing agent including primary and secondary
diamines or polyamines in which the radicals attached to the
nitrogen atoms can be saturated or unsaturated, aliphatic,
alicyclic, aromatic, aromatic-substituted aliphatic,
aliphatic-substituted aromatic, or heterocyclic. In other
embodiments, the polyamine curing agent may include mixed amines in
which the radicals are different such as, for example, aromatic
groups, aliphatic groups, and other non-reactive groups attached to
the carbon atoms such as oxygen, sulfur, halogen, or nitro groups.
Examples of suitable aliphatic and alicyclic diamines include
1,2-ethylene diamine, 1,2-propylene diamine, 1,8-p-menthane
diamine, isophorone diamine, propane-2,2-cyclohexyl amine, and
methane-bis-(4-cyclohexyl amine), and
H.sub.2N--(--CH.sub.2--(CHCH.sub.3--O--).sub.x--CH.sub.2--CHCH.sub.3--NH.s-
ub.2
[0063] where x is from 1 to 10.
[0064] The polyamine curing agent includes phenylene diamines and
toluene diamines such as, for example, o-phenylene diamine and
p-tolylene diamine, and N-alkyl and N-aryl derivatives thereof,
such as, for example, N,N'-dimethyl-o-phenylene diamine,
N,N'-di-p-tolyl-m-phenylene diamine, and p-amino-diphenylamine.
[0065] The polyamine curing agent may be a polynuclear aromatic
diamine in which the aromatic rings are attached by means of a
valence bond such as, for example, 4,4'-biphenyl diamine, methylene
dianiline, and monochloromethylene dianiline.
[0066] Epoxy-capped polythioethers of the invention may be used in
curable compositions, such as sealants, coatings, and adhesives,
either alone or in combination with other resins. In certain
embodiments, curable compositions of the invention may include
fillers and additives as appropriate for specific applications.
[0067] Fillers may be added to curable compositions of the
invention to impart desirable physical properties such as, for
example, to increase the impact strength, to control the viscosity,
to modify the electrical properties, or to reduce the specific
gravity. Fillers useful in the curable compositions of the
invention for aviation and aerospace applications include those
commonly used in the art, such as carbon black, calcium carbonate,
silica, and polymer powders. Exemplary fillers include
Sipernat.RTM. D-13 hydrophobic precipitated silica (Degussa),
Winnofil.RTM. SPM precipitated calcium carbonate (Solvay
Chemicals), TS-270 (Cabot Corporation), titanium dioxide (DuPont),
aluminum hydroxide, and Orgasol.RTM. 1002 D Nat 1 ultrafine
polyamide powder (Atofina Chemicals). In certain embodiments, the
filler comprises from 5% by weight to 60% by weight of the
non-volatile components of the curable composition.
[0068] The curable compositions of the invention usually comprise
at least one additive selected from the following: plasticizers,
pigments, cure accelerators, adhesion promoters, thixotropic
agents, fire retardants, masking agents, antioxidants, and
surfactants. The additive may be present in the curable composition
in amounts of 0.1 to 40% by weight based on the total weight of the
curable composition.
[0069] The plasticizer may include at least one of the following:
phthalate esters, chlorinated paraffins, and hydrogenated
terphenyls. Examples of useful plasticizers include HB-40.RTM.
modified polyphenyl (Solutia, Inc.) and tung oil (Campbell &
Co.). In certain embodiments, the plasticizer comprises from 1% by
weight to 40% by weight of the total weight of the curable
composition, more typically from 1% by weight to 8% by weight of
the total weight of the curable composition.
[0070] The curable compositions of the invention may comprise at
least one pigment. Examples of pigment include at least one of the
following: carbon black, metal oxides, and calcium carbonate.
Pigment grade carbon black generally is characterized by low
structure and particle size such as Regal.RTM. 660R (Cabot
Corporation). Brilliant 1500 is an example of pigment grade,
99.995+%, calcium carbonate (Aldrich Chemical). In certain
embodiments, the pigment comprises from 0.1% by weight to 10% by
weight of the total weight of the curable composition. In other
embodiments, the pigment comprises from 0.1% by weight to 5% by
weight of the total weight of the curable composition.
[0071] Curable compositions of the invention are cured according to
recommended procedures and, in certain embodiments, at ambient
temperature. "Curable" refers to the capability of undergoing one
or more chemical reactions to form stable, covalent bonds among the
constituent components. The curable compositions are usually
curable at a minimum temperature of 50.degree. C. to 100.degree. C.
and more typically from 60.degree. C. to 75.degree. C.
EXAMPLES
[0072] Reference will now be made in detail to specific embodiments
of the invention. While certain embodiments of the invention will
be described in conjunction with the preferred embodiments, it will
be understood that it is not intended to limit the embodiment of
the invention to those preferred embodiments. To the contrary, it
is intended to cover alternatives, modifications, and equivalents
as may be included within the spirit and scope of the embodiments
of the invention as defined by the appended claims.
[0073] The following tests were used to characterize certain
curable compositions of the invention:
[0074] Chemical resistance was determined according to ASTM D 1308,
24 Hour Spot Test.
[0075] Hardness was determined according to NMS 332 4.4.18 and AMS
3277 4.5.5.
[0076] Viscosity was determined according to MMS 332 4.4.4 and AMS
3277 4.5.8.
[0077] Odor was determined empirically.
[0078] Color was determined according to Gardner method.
[0079] Epoxy equivalent weight was determined according to ASTM
1652.
[0080] Tensile strength was determined according to ASTM D 412.
[0081] Elongation was determined according to ASTM D 412.
Example 1
[0082] 253.4 g (1.39 mole) of dimercaptodioxaoctane (DMDO) was
added to a 1 liter 4-neck flask under a nitrogen atmosphere. While
stirring, the contents of the flask was heated to 50.degree. C.,
and 146.6 g (0.93 mole) of diethylene glycol divinyl ether
(DEG-DVE) was added over 1 hr. The temperature of the reaction
mixture was increased to 70.degree. C. and 0.05 g of free-radical
initiator Vazo.RTM.67 (2,2'-azobis(2-methylbut- yronitrile), Du
Pont) was added. The temperature of the reaction mixture was
maintained at 70.degree. C. for an additional hour. Completion of
the reaction of DEG-DVE with DMDO was indicated by a mercaptan
equivalent value of 420. Allyl glycidyl ether (AGE) (110.87 g, 0.97
mole, 2% stoichiometric excess) was added at 70.degree. C. over 1
hr and the reaction mixture was heated at 70.degree. C. for an
additional hour. Ten portions of Vazo.RTM.67 (0.165 g each) were
then added at 3 hr intervals at 70.degree. C. Following addition of
Vazo.RTM.67 the reaction mixture was heated at 70.degree. C. for 5
hr. The reaction mixture was then degassed at 70.degree. C./4-5 mm
Hg for 3 hr to provide a liquid epoxy-capped polythioether having a
faint yellow color, a viscosity of 5.0 poise, and an epoxy
equivalent value of 563. The reaction yield was 508.7 g (100%).
Example 2
[0083] 62.17 g (moles) of DMDO was added to a 250 ml 3-neck flask
under a nitrogen atmosphere. While stirring, DMDO was heated to
60.degree. C. and 44.88 g (mole) of DEG-DVE was added to the
reaction mixture over a period of 50 minutes while the temperature
of the reaction was maintained at 60.degree. C.-70.degree. C. The
reaction mixture was heated at 70.degree. C. for an additional 4
hr. Two portions of Vazo.RTM.67 (0.036 g each) were added to the
reaction mixture at 1.5 hr intervals and heated at 70.degree. C.
for 1.5 hr. The mercaptan equivalent value of the reaction mixture
was 890. An additional portion of Vazo.RTM.67 (0.036 g) was added
and the reaction mixture heated for another 1.5 hr. A mercaptan
equivalent value of 893 indicated completion of the reaction of
DEG-DVE with DMDO. AGE (13.21 g, 0.116 mole, 2% stoichiometric
excess) was added at 70.degree. in one portion and the reaction
mixture was heated for 2 hr. Eight portions of Vazo.RTM.67 (0.035 g
each) were added at 3 hr intervals at 70.degree. C. and heating was
continued for another 4 hr. At this stage, the mercaptan equivalent
value of the reaction mixture was of 28,642. To complete the
reaction, an additional 4.8 g (0.042 mole, 38% stoichiometric
excess) of AGE was added and the reaction mixture was heated for 1
hr at 70.degree. C. Two portions of Vazo.RTM.67 (0.036 g each) were
added at 3 hr intervals. Following the addition of Vazo.RTM.67, the
reaction mixture was heated at 70.degree. C. for 5 hours. The
reaction mixture was then degassed at 70.degree. C./4-5 mm Hg for 2
hr to provide a slightly hazy, liquid epoxy-capped polythioether
having a faint yellow color, a viscosity of 26 poise, and an epoxy
equivalent value of 1,217. The reaction yield was 120.0 g
(100%).
[0084] Curable Composition 1 was prepared by combining 12.5 parts
by weight of the epoxy-capped polythioether of Example 1, 37.5
parts by weight of Epon 828, 28 to 29 parts by weight of Epi-Cure
3155, and 0.5 parts by weight of DMP 30. Curable composition 1 was
cured at a temperature of 68.degree. F. for one week. A summary of
the properties of cured Composition 1 is presented in Table 1.
1TABLE 1 Properties of Cured Composition 1. Property Composition 1
Physical state Clear amber Liquid Odor none Color 3 max Viscosity
at 25.degree. C. (poise) 5 Specific Gravity 1.13 Epoxy Equivalent
Value 530-650 Tg, DSC (.degree. C.) -42.0 .+-. 1.0 Gel Time
(minutes) 196 Compatibility with Good epoxy/ECA HYC none Chemical
Resistance: (24 Hour Spot Test) 10% H.sub.2SO.sub.4 Excellent 10%
Acetic Acid Excellent 10% HCl Excellent 2% HNO.sub.3 Some Yellowing
10% NaOH Excellent Skydrol Excellent Xylene Excellent Hardness,
pencil 2H Tensile Strength 1125 pli Elongation 2.07%
[0085] When cured, curable Composition 1 exhibits excellent
chemical resistance, including excellent resistance to aviation and
aerospace fuels.
[0086] The viscosity of curable Composition 1 of 5 poise at a
temperature of 25.degree. C. is six times less than
epoxy-terminated polysulfides produced using epichlorohydrin. The
low viscosity of the epoxy-capped polythioethers of the invention
provide greater latitude in producing formulations than comparable
compositions prepared with epoxy-terminated polysulfides produced
using epichlorohydrin. Other desirable attributes include a low
specific gravity of 1.13, a low epoxy equivalent weight of from 530
to 650, and the epoxy-capped polythioethers are compatible with
amines and other epoxy compounds.
* * * * *