U.S. patent application number 09/815137 was filed with the patent office on 2002-01-03 for novel fluorovinyl ether cure site monomers and fluoroelastomer copolymer compositions thereof.
Invention is credited to Hung, Ming-Hong, Schmiegel, Walter W..
Application Number | 20020002258 09/815137 |
Document ID | / |
Family ID | 56290127 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020002258 |
Kind Code |
A1 |
Hung, Ming-Hong ; et
al. |
January 3, 2002 |
Novel fluorovinyl ether cure site monomers and fluoroelastomer
copolymer compositions thereof
Abstract
Disclosed herein is a novel class of fluorovinyl ether monomers
which are useful as cure site monomers in fluoroelastomers, a
process for the preparation of these fluorovinyl ether monomers,
and fluoroelastomer copolymer compositions that contain
copolymerized units of these fluorovinyl ether monomers.
Inventors: |
Hung, Ming-Hong;
(Wilmington, DE) ; Schmiegel, Walter W.;
(Wilmington, DE) |
Correspondence
Address: |
DUPONT DOW ELASTOMERS, LLC
LEGAL DEPARTMENT -- PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
56290127 |
Appl. No.: |
09/815137 |
Filed: |
March 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60198351 |
Apr 19, 2000 |
|
|
|
Current U.S.
Class: |
526/247 ;
568/615 |
Current CPC
Class: |
C08F 214/222 20130101;
C07C 43/17 20130101; C08F 216/1408 20130101 |
Class at
Publication: |
526/247 ;
568/615 |
International
Class: |
C08F 016/24; C08F
116/12; C08F 216/12; C07C 043/11; C07C 043/18; C07C 043/20 |
Claims
What is claimed is:
1. A fluorovinyl ether monomer having the formula
CF.sub.3CHFCF.sub.2--(O)-
.sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOCF.dbd.CF.sub.2,
wherein R.sub.f is a C.sub.1-C.sub.8 perfluoroalkyl group or a
C.sub.1-C.sub.8 perfluoroalkoxy group, n is 0 or 1, m is an integer
from 1 to 3, and p is an integer from 1 to 4.
2. A fluorovinyl ether monomer of claim 1 wherein R.sub.f is
--[OCF(CF.sub.3)CF.sub.2]--, and wherein x is 1 or 2; n is 1, m is
1 and p is an integer from 1 to 4.
3. A fluorovinyl ether monomer of claim 2 of the formula
CF.sub.3CHFCF.sub.2--O--CH.sub.2CF.sub.2CF.sub.2--O--CF(CF.sub.3)CF.sub.2-
--OCF.dbd.CF.sub.2.
4. A process for the preparation of a fluorovinyl ether monomer
having the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.-
p--R.sub.fOCF.dbd.CF.sub.2, wherein R.sub.f is a C.sub.1-C.sub.8
perfluoroalkyl group or a C.sub.1-C.sub.8 perfluoroalkoxy group, n
is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1
to 4; said process comprising the steps of: A. chlorinating an
hydroxy vinyl ether compound of the formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOC- F.dbd.CF.sub.2
to produce a chlorinated hydroxy ether of the formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOCFCl--CF.sub.2Cl;
B. condensing said chlorinated hydroxy ether with hexafluoropropene
to produce a chlorinated ether of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n-
--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOCFCl--CF.sub.2Cl; and
C. dechlorinating said chlorinated ether to produce a fluorinated
vinyl ether of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(C-
F.sub.2).sub.p--R.sub.f--OCF.dbd.CF.sub.2.
5. A process of claim 4 wherein said hydroxy vinyl ether compound
is chlorinated by reaction with neat chlorine at a temperature
between -15 to 40.degree. C.
6. A process of claim 4 wherein said chlorinated hydroxy ether is
condensed with hexafluoropropylene at a temperature between -15 to
70.degree. C. in the presence of a strong base in an aprotic
solvent.
7. A process of claim 6 wherein said aprotic solvent is anhydrous
dimethylsulfoxide and said base is potassium t-butoxide.
8. A process of claim 4 wherein said chlorinated ether is
dechlorinated by reaction with a reducing agent in an aprotic
solvent at a temperature between 70 to 140.degree. C.
9. A process of claim 8 wherein said reducing agent is zinc dust
and said aprotic solvent is dimethylformamide.
10. A fluoroelastomer copolymer comprising: A. copolymerized units
of a first monomer, said first monomer being a fluoroolefin
selected from the group consisting of vinylidene fluoride and
tetrafluoroethylene; B. copolymerized units of a second monomer,
different from said first monomer, said second monomer selected
from the group consisting of i) fluoroolefins, ii) hydrocarbon
olefins, iii) perfluoro(alkyl vinyl)ethers and iv) perfluoro(alkoxy
vinyl) ethers; and C. copolymerized units of a fluorinated vinyl
ether cure site monomer of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub-
.fOCF.dbd.CF.sub.2, wherein R.sub.f is a C.sub.1-C.sub.8
perfluoroalkyl group or a C.sub.1-C.sub.8 perfluoroalkoxy group, n
is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1
to 4.
11. A fluoroelastomer copolymer of claim 10 wherein said first
monomer is vinylidene fluoride and said second monomer is
hexafluoropropylene.
12. A fluoroelastomer copolymer of claim 11 further comprising
copolymerized units of tetrafluoroethylene.
13. A fluoroelastomer copolymer of claim 10 wherein said first
monomer is vinylidene fluoride and said second monomer is
perfluoro(methyl vinyl) ether.
14. A fluoroelastomer copolymer of claim 13 further comprising
copolymerized units of tetrafluoroethylene.
15. A fluoroelastomer copolymer of claim 10 wherein said first
monomer is tetrafluoroethylene and said second monomer is
propylene.
16. A fluoroelastomer copolymer of claim 15 further comprising
copolymerized units of vinylidene fluoride.
17. A fluoroelastomer copolymer of claim 10 wherein said first
monomer is tetrafluoroethylene, said second monomer is ethylene and
further comprising copolymerized units of perfluoro(methyl vinyl)
ether.
18. A curable composition comprising: A. a fluoroelastomer
comprising copolymerized units of a first monomer, said first
monomer being a fluoroolefin selected from the group consisting of
vinylidene fluoride and tetrafluoroethylene; copolymerized units of
a second monomer, different from said first monomer, said second
monomer selected from the group consisting of i) fluoroolefins, ii)
hydrocarbon olefins, iii) perfluoro(alkyl vinyl)ethers and iv)
perfluoro(alkoxy vinyl) ethers; and copolymerized units of a
fluorinated vinyl ether cure site monomer of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.-
p--R.sub.f--OCF.dbd.CF.sub.2, wherein R.sub.f is a C.sub.1-C.sub.8
perfluoroalkyl group or a C.sub.1-C.sub.8 perfluoroalkoxy group, n
is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1
to 4; B. a polyhydroxy crosslinking agent; C. a cure accelerator;
and D. a metal oxide or metal hydroxide.
19. A fluoroelastomer copolymer of claim 18 wherein said first
monomer is vinylidene fluoride and said second monomer is
hexafluoropropylene.
20. A fluoroelastomer copolymer of claim 19 further comprising
copolymerized units of tetrafluoroethylene.
21. A fluoroelastomer copolymer of claim 18 wherein said first
monomer is vinylidene fluoride and said second monomer is
perfluoro(methyl vinyl) ether.
22. A fluoroelastomer copolymer of claim 21 further comprising
copolymerized units of tetrafluoroethylene.
23. A fluoroelastomer copolymer of claim 18 wherein said first
monomer is tetrafluoroethylene and said second monomer is
propylene.
24. A fluoroelastomer copolymer of claim 23 further comprising
copolymerized units of vinylidene fluoride.
25. A fluoroelastomer copolymer of claim 18 wherein said first
monomer is tetrafluoroethylene, said second monomer is ethylene and
further comprising copolymerized units of perfluoro(methyl vinyl)
ether.
26. A composition of claim 18 wherein the polyhydroxy crosslinking
agent B is a crosslinking agent selected from the group consisting
of i) dihydroxy-, trihydroxy-, and tetrahydroxy-benzenes,
-naphthalenes, and -anthracenes; ii) bisphenols of the formula
2where A is a stable divalent radical; x is 0 or 1; and n is 1 or
2; iii) dialkali salts of said bisphenols, iv) quaternary ammonium
and phosphonium salts of said bisphenols, v) tertiary sulfonium
salts of said bisphenols, and vi) esters of phenols.
27. A curable composition of claim 18 wherein said cure accelerator
is selected from the group consisting of quaternary ammonium salts,
tertiary sulfonium salts and quaternary phosphonium salts.
28. A curable composition of claim 18 wherein said cure accelerator
C is selected from the group consisting of i) quaternary ammonium
salts of the polyhydroxy crosslinking agent (B), ii) quaternary
phosphonium salts of the polyhydroxy crosslinking agent (B) and
iii) tertiary sulfonium salts of the polyhydroxy crosslinking
agent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/198,351 filed Apr. 19, 2000.
FIELD OF THE INVENTION
[0002] This invention relates to a novel class of fluorovinyl ether
monomers which are useful as cure site monomers in
fluoroelastomers, a process for the preparation of these
fluorovinyl ether monomers and to curable fluoroelastomer
copolymers having copolymerized units of these fluorovinyl ether
monomers.
BACKGROUND OF THE INVENTION
[0003] Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit
excellent resistance to the effects of heat, weather, oil, solvents
and chemicals. Such materials are commercially available and are
most commonly either dipolymers of vinylidene fluoride (VF.sub.2)
with hexafluoropropylene (HFP) or terpolymers of VF.sub.2, HFP, and
tetrafluoroethylene (TFE). While these di- and terpolymers have
many desirable properties, including low compression set and
excellent processability, their low temperature flexibility is not
adequate for all applications, nor is their resistance to attack by
alkaline solvents.
[0004] It is known that incorporation of perfluorinated ether
monomer units into vinylidene fluoride elastomers improves low
temperature properties, i.e. cured articles made from these
polymers seal well at low temperatures. For example, Carlson, in
U.S. Pat. No. 5,214,106 discloses that when perfluoro(methyl vinyl)
ether (PMVE) is substituted for HFP, the resultant
VF.sub.2/PMVE/TFE copolymers have glass transition temperature
(T.sub.g) values which are 10.degree.-20.degree. C. lower than
those of the corresponding VF.sub.2/HFP/TFE copolymers. T.sub.g is
often used as an indicator of low temperature flexibility because
polymers having low glass transition temperatures maintain
elastomeric properties at low temperatures.
[0005] Other common fluoroelastomers include the copolymers of TFE
with one or more hydrocarbon olefins such as ethylene or propylene,
and, optionally VF.sub.2 (for example U.S. Pat. No. 4,758,618).
These copolymers are generally more resistant to attack by alkaline
solutions than other types of fluoroelastomers. The copolymers may
also contain a perfluoro(alkyl vinyl) ether (PAVE) in order to
impart good low temperature sealing properties (U.S. Pat. No.
4,694,045).
[0006] Many of the fluoroelastomers listed above require
incorporation of a cure site monomer into their polymer chains in
order to crosslink efficiently. Without such a cure site monomer,
the fluoroelastomer may not react at all with curing agents, it may
only partially react, or reaction may be too slow for use on a
commercial scale. Seals made from poorly crosslinked elastomers
often fail sooner than might otherwise be expected. Unfortunately,
disadvantages are associated with many of the cure site monomers in
use today. For example, monomers which contain reactive bromine or
iodine atoms can release byproducts during the curing reaction that
are harmful to the environment. Other cure site monomers (e.g.
those which contain double bonds at both ends of the molecule) may
be so reactive that they disrupt polymerization of the
fluoroelastomer by altering the polymerization rate, terminating
polymerization, or by causing undesirable chain branching, or even
gelation to occur. Lastly, incorporation of a cure site monomer
into a fluoroelastomer polymer chain may negatively impact the
properties of the fluoroelastomer (both physical properties and
chemical resistance).
[0007] There thus exists a need in the art for cure site monomers
which are environmentally friendly, do not disrupt polymerization
and which do not detract from the properties of the
fluoroelastomer.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a fluorovinyl ether
monomer of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).-
sub.p--R.sub.f--OCF.dbd.CF.sub.2, wherein R.sub.f is a
C.sub.1-C.sub.8 perfluoroalkyl group or a C.sub.1-C.sub.8
perfluoroalkoxy group, n is 0 or 1, m is an integer from 1 to 3,
and p is an integer from 1 to 4.
[0009] The present invention is also directed to a process for the
preparation of the above fluorovinyl ether. The process comprises
the steps of
[0010] A. chlorinating an hydroxy vinyl ether compound of the
formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOCF.dbd.CF.sub.2 to
produce a chlorinated hydroxy ether of the formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.fOCFCl--CF.sub.2Cl;
[0011] B. condensing said chlorinated hydroxy ether with
hexafluoropropene to produce a chlorinated ether of the formula
CF.sub.3CHFCF.sub.2--(O).su-
b.n--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.f--OCFCl--CF.sub.2Cl;
and
[0012] C. dechlorinating said chlorinated ether to produce a
fluorinated vinyl ether of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub-
.m---(CF.sub.2).sub.p--R.sub.f--OCF.dbd.CF.sub.2.
[0013] The present invention is also directed to a fluoroelastomer
composition comprising
[0014] A. copolymerized units of a first monomer, said first
monomer being a fluoroolefin selected from the group consisting of
vinylidene fluoride and tetrafluoroethylene;
[0015] B. copolymerized units of a second monomer, different from
said first monomer, said second monomer selected from the group
consisting of i) fluoroolefins, ii) hydrocarbon olefins, iii)
perfluoro(alkyl vinyl)ethers and iv) perfluoro(alkoxy vinyl)
ethers; and
[0016] C. copolymerized units of a fluorinated vinyl ether cure
site monomer of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m---
(CF.sub.2).sub.p--R.sub.f--OCF.dbd.CF.sub.2, wherein R.sub.f is a
C.sub.1-C.sub.8 perfluoroalkyl group or a C.sub.1-C.sub.8
perfluoroalkoxy group, n is 0 or 1, m is an integer from 1 to 3,
and p is an integer from 1 to 4.
[0017] The present invention is also directed to a polyhydroxylic
curable composition of the above fluoroelastomer.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The fluoroelastomers utilized in the curable compositions of
the present invention are copolymers capable of undergoing
crosslinking reactions with polyhydroxylic compounds to form cured
elastomeric compositions that exhibit excellent physical properties
and chemical resistance. Furthermore, the cure site monomers
employed in the fluoroelastomers of this invention do not adversely
affect the polymerization process, nor do byproducts of the curing
reaction pose an environmental concern.
[0019] The fluoroelastomers of this invention comprise
copolymerized units of A) a first monomer which is a fluoroolefin
selected from the group consisting of vinylidine fluoride and
tetrafluoroethylene; B) a second monomer, which is not the same as
the first monomer, and which is selected from the group consisting
of fluoroolefins, hydrocarbon olefins, perfluoro(alkyl vinyl)ethers
and perfluoro(alkoxy vinyl) ethers; and C) a fluorovinyl ether cure
site monomer of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub-
.fOCF.dbd.CF.sub.2, wherein R.sub.f is a C.sub.1-C.sub.8
perfluoroalkyl group or a C.sub.1-C.sub.8 perfluoroalkoxy group, n
is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1
to 4.
[0020] Optionally, the fluoroelastomers of this invention may
further comprise copolymerized units of at least one additional
monomer, different from said first, second and cure site monomers.
The additional monomer or monomers may be selected from the group
consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy
vinyl) ethers, fluoroolefins and hydrocarbon olefins.
[0021] In addition, the fluoroelastomer copolymers of this
invention may optionally contain up to about 1 wt. % iodine bound
to polymer chain ends, the iodine being introduced via use of an
iodine-containing chain transfer agent during polymerization.
[0022] Examples of fluoroolefin monomers useful as the second
monomer and as the optional additional monomer in the
fluoroelastomers of this invention include, but are not limited to
vinylidene fluoride (VF.sub.2), tetrafluoroethylene (TFE),
chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP),
pentafluoropropylene, vinyl fluoride and the like.
[0023] Hydrocarbon olefin monomers which may be employed as the
second monomer and as the optional additional monomer in
fluoroelastomers of this invention contain no fluorine atoms.
Examples of such hydrocarbon olefins include, but are not limited
to ethylene (E), propylene (P), butylene-1 and isobutylene.
[0024] Perfluoro(alkyl vinyl) ethers suitable for use as comonomers
include those of the formula
CF.sub.2.dbd.CFO(R.sub.f'O).sub.n(R.sub.f"O).sub.mR.sub.f (I)
[0025] where R.sub.f' and R.sub.f" are different linear or branched
perfluoroalkylene groups of 2-6 carbon atoms, m and n are
independently 0-10, and R.sub.f is a perfluoroalkyl group of 1-6
carbon atoms.
[0026] A preferred class of PAVE includes compositions of the
formula
CF.sub.2.dbd.CFO(CF.sub.2CFXO).sub.nR.sub.f (II)
[0027] where X is F or CF.sub.3, n is 0-5, and R.sub.f is a
perfluoroalkyl group of 1-6 carbon atoms. A most preferred class of
PAVE includes those ethers wherein n is 0 or 1 and R.sub.f contains
1-3 carbon atoms. Examples of such perfluorinated ethers include
perfluoro(methyl vinyl) ether and perfluoro(propyl vinyl) ether.
Other useful monomers include compounds of the formula
CF.sub.2.dbd.CFO [(CF.sub.2).sub.mCF.sub.2CFZO].sub.nR.sub.f
(III)
[0028] where R.sub.f is a perfluoroalkyl group having 1-6 carbon
atoms,
[0029] m=0 or 1, n=0-5, and Z=F or CF.sub.3.
[0030] Preferred members of this class are those in which R.sub.f
is C.sub.3F.sub.7, m=0, and n=1.
[0031] Additional perfluoro(alkyl, vinyl) ether monomers include
compounds of the formula
CF.sub.2.dbd.CFO[(CF.sub.2CFCF.sub.3O).sub.n(CF.sub.2CF.sub.2CF.sub.2O).su-
b.m(CF.sub.2).sub.p]C.sub.xF.sub.2x+1 (IV)
[0032] where m and n independently=1-10, p=0-3, and x=1-5.
[0033] Preferred members of this class include compounds where
n=0-1, m=0-1, and x=1.
[0034] Examples of useful perfluoro(alkoxy vinyl) ethers
include
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)O(CF.sub.2O).sub.mC.sub.nF.sub.2n+1
(V)
[0035] where n=1-5, m=1-3, and where, preferably, n=1.
[0036] Mixtures of perfluoro(alkyl vinyl) ethers and
perfluoro(alkoxy vinyl) ethers may also be used.
[0037] Specific examples of the fluoroelastomers of this invention
include, but are not limited to polymers having copolymerized units
of the fluorovinyl ether cure site monomers of this invention and
units of VF.sub.2/HFP; VF.sub.2/HFP/TFE; VF.sub.2/PMVE;
VF.sub.2/PMVE/TFE; TFE/P; TFE/P/VF.sub.2; and E/TFE/PMVE.
[0038] The cure site monomers useful in the fluoroelastomers of
this invention are a class of fluorovinyl ethers having the general
formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub-
.f--OCF.dbd.CF.sub.2, wherein R.sub.f is a C.sub.1-C.sub.8
perfluoroalkyl group or a C.sub.1-C.sub.8 perfluoroalkoxy group, n
is 0 or 1, m is an integer from 1 to 3, and p is an integer from 1
to 4. Preferably R.sub.f is --[OCF(CF.sub.3)CF.sub.2].sub.x--,
wherein x is 1 or 2; n is 1, m is 1 and p is an integer from 1 to
4. A specific example of these fluorovinyl ethers includes, but is
not limited to CF.sub.3CHFCF.sub.2--O--CH.sub.2CF-
.sub.2CF.sub.2--O--CF(CF.sub.3)CF.sub.2--OCF=CF.sub.2.
[0039] These cure site monomers polymerize into the fluoroelastomer
polymer chain through their vinyl group, resulting in copolymerized
units having pendant
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(CF.sub.-
2).sub.p--R.sub.f--O-- side chains. During curing, the side chains
may readily dehydrofluorinate to form carbon-carbon double bonds.
These sites of unsaturation then act as cure sites for
crosslinking.
[0040] A particular characteristic of the cure site monomer of this
invention is that it acts as an independent cure site monomer that
takes part in crosslinking reactions with polyhydroxylic curing
agents. That is, polymers that contain copolymerized units of this
cure site monomer do not require the presence of copolymerized
VF.sub.2 monomer sequences flanked by perfluoromonomers (e.g.
HFP/VF.sub.2/HFP) for initiation of dehydrofluorination.
[0041] Because of the ease of hydrogen abstraction in the
fluoroelastomer copolymers of this invention, the copolymers need
contain only low levels of cure site monomer, i.e. 0.3-5 wt. %
(preferably 0.7-3 wt. %), to promote efficient polyhydroxylic
cures. This permits adjustment of other comonomer levels to
maximize particular physical properties. Thus, the polymers of the
present invention exhibit excellent cure characteristics when only
low levels of cure site monomer are present.
[0042] The fluorovinyl ether monomers of this invention may be
prepared by a process comprising the steps of a) chlorinating an
hydroxy vinyl ether compound of the formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.f--- OCF.dbd.CF.sub.2
to produce a chlorinated hydroxy ether of the formula
HO--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.f--OCFCl--CF.sub.2Cl;
b) condensing said chlorinated hydroxy ether with hexafluoropropene
to produce a chlorinated ether of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n-
--(CH.sub.2).sub.m--(CF.sub.2).sub.p--R.sub.f--OCFCl--CF.sub.2Cl;
and c) dechlorinating said chlorinated ether to produce a
fluorinated vinyl ether of the formula
CF.sub.3CHFCF.sub.2--(O).sub.n--(CH.sub.2).sub.m--(C-
F.sub.2).sub.p--R.sub.f--OCF.dbd.CF.sub.2. A preferred means for
dechlorinating is by reaction with a reducing agent (such as zinc)
in an aprotic solvent at a temperature between 70 to 140.degree. C.
The hydroxy vinyl ether starting material is known in the art. Some
of these hydroxy vinyl ethers are available commercially from
DuPont, or they may be synthesized by the process disclosed in U.S.
Pat. No. 4,982,009.
[0043] In the above process, the hydroxy vinyl ether may be
chlorinated by a variety of means including by the reaction with
neat chlorine at a temperature between -15 to 40.degree. C.,
preferably 0 to 10.degree. C.
[0044] The chlorinated hydroxy ether may be condensed with
hexafluoropropene by a variety of means, including by the reaction
at a temperature between -15 to 70.degree. C. of
hexafluoropropylene with the chlorinated vinyl ether contained in
an anhydrous aprotic solvent and in the presence of a strong base.
Suitable aprotic solvents include dimethylsufoxide and
dimethylformamide. Suitable strong bases include potassium
t-butoxide.
[0045] The polymers of this invention may be prepared using free
radical batch or semi-batch, or continuous free radical emulsion
polymerization processes. They may also be prepared by free radical
suspension polymerization processes.
[0046] For example, if a continuous emulsion process is utilized,
the polymers are generally prepared in a continuous stirred tank
reactor. Polymerization temperatures may be in the range of
40.degree. to 145.degree. C., preferably 80.degree. to 135.degree.
C. at pressures of 1 to 8 MPa. Residence times of 20 to 360 minutes
are preferred. Free radical generation may be effected through use
of a water-soluble initiator such as ammonium persulfate, either by
thermal decomposition or by reaction with a reducing agent such as
sodium sulfite. An inert surface-active agent such as ammonium
perfluorooctanoate may be utilized to stabilize the dispersion,
usually in conjunction with addition of a base such as sodium
hydroxide or a buffer such as disodium phosphate to control pH in
the range 3 to 7. Unreacted monomer is removed from the reactor
effluent latex by vaporization at reduced pressure. Polymer is
recovered from the stripped latex by coagulation. For example,
coagulation may be effected by reducing latex pH to about 3 by
addition of acid, then adding a salt solution, such as an aqueous
solution of calcium nitrate, magnesium sulfate, or potassium
aluminum sulfate, to the acidified latex. The polymer is separated
from the serum, then washed with water and subsequently dried.
After drying, the product may be cured.
[0047] Chain transfer agents may be used in the polymerization in
order to control the molecular weight distribution of the resulting
polymers. Examples of chain transfer agents include isopropanol;
methyl ethyl ketone; ethyl acetate; diethyl malonate; isopentane;
1,3-diiodoperfluoropropane; 1,4-diiodoperfluorobutane;
1,6-diiodoperfluorohexane; 1,8-diiodoperfluorooctane; methylene
iodide; trifluoromethyl iodide; perfluoro(isopropyl) iodide; and
perfluoro(n-heptyl) iodide. Polymerization in the presence of
iodine-containing chain transfer agents may result in a polymer
with one or two iodine atoms per fluoroelastomer polymer chain,
bound at the chain ends (see for example U.S. Pat. Nos. 4,243,770
and 4,361,678). Such polymers may have improved flow and
processability compared to polymers made in the absence of a chain
transfer agent. Generally, up to about 1 weight percent iodine
chemically bound to fluoroelastomer chain ends will be incorporated
into the polymer, preferably from 0.1-0.3 wt. %.
[0048] An embodiment of the present invention is a curable
composition that comprises the above-described copolymers and a
polyhydroxylic curing agent. The polymers of the invention are also
curable with amines and amine derivatives (e.g. carbamates).
[0049] Any of the known aromatic polyhydroxylic crosslinking agents
that require accelerators for satisfactory cure rates are suitable
for use with the fluoroelastomers of the present invention. The
crosslinking agent is usually added in amounts of from about 0.5-4
parts by weight per hundred parts by weight fluoroelastomer (phr),
usually 1-2.5 phr. Preferred crosslinking agents are di- tri-,
tetrahydroxybenzenes, naphthalenes, anthracenes and bisphenols of
the formula 1
[0050] where A is a stable divalent radical, such as a difunctional
aliphatic, cycloaliphatic, or aromatic radical of 1- 13 carbon
atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonyl radical; A
is optionally substituted with at least one chlorine or fluorine
atom; x is 0 or 1; n is 1 or 2 and any aromatic ring of the
polyhydroxylic compound is optionally substituted with at least one
atom of chlorine, fluorine, or bromine, a --CHO group, or a
carboxyl or acyl radical (e.g. a --COR where R is OH or a
C.sub.1-C.sub.8 alkyl, aryl, or cycloalkyl group). It will be
understood from the above formula describing bisphenols that the
--OH groups can be attached in any position (other than number one)
in either ring. Blends of two or more such compounds can also be
used.
[0051] Referring to the bisphenol formula shown in the previous
paragraph, when A is alkylene, it can be, for example, methylene,
ethylene, chloroethylene, fluoroethylene, difluoroethylene,
1,3-propylene, 1,2-propylene, tetramethylene, chlorotetramethylene,
fluorotetramethylene, trifluorotetramethylene,
2-methyl-1,3-propylene, 2-methyl-1,2-propylene, pentamethylene, and
hexamethylene. When A is alkylidene, it can be for example
ethylidene, dichloroethylidene, difluoroethylidene, propylidene,
isopropylidene, trifluoroisopropylidene, hexafluoroisopropylidene,
butylidene, heptachlorobutylidene, heptafluorobutylidene,
pentylidene, hexylidene, and 1,1-cyclohexylidene. When A is a
cycloalkylene radical, it can be for example 1,4-cyclohexylene,
2-chloro-1,4-cyclohexylene, 2-fluoro-1,4-cyclohexylene- ,
1,3-cyclohexylene, cyclopentylene, chlorocyclopentylene,
fluorocyclopentylene, and cycloheptylene. Further, A can be an
arylene radical such as m-phenylene, p-phenylene,
2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene, o-phenylene,
methylphenylene, dimethylphenylene, trimethylphenylene,
tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene,
5-chloro-1,4-naphthylene, 1,5-naphthylene, and 2,6-naphthylene.
Bisphenol AF (4,4'-(hexafluoroisopropylidene)diphenol) is a
preferred crosslinking agent.
[0052] Other useful crosslinking agents include hydroquinone,
dihydroxybenzenes such as catechol, resorcinol, 2-methyl
resorcinol, 5-methyl resorcinol, 2-methyl hydroquinone,
2,5-dimethyl hydroquinone; 2-t-butyl hydroquinone; and
1,5-dihydroxynaphthalene.
[0053] Additional polyhydroxy curing agents include alkali metal
salts of bisphenol anions, quaternary ammonium salts of bisphenol
anions and quaternary phosphonium salts of bisphenol anions. For
example, the salts of bisphenol A and bisphenol AF. Specific
examples include the disodium salt of bisphenol AF, the dipotassium
salt of bisphenol AF, the monosodium monopotassium salt of
bisphenol AF and the benzyltriphenylphosphonium salt of bisphenol
AF. Quaternary ammonium and phosphonium salts of bisphenol anions
and their preparation are discussed in U.S. Pat. Nos. 4,957,975 and
5,648,429.
[0054] In addition, derivatized polyhydroxy compounds, such as
diesters, are useful crosslinking agents. Examples of such
compositions include diesters of phenols, such as the diacetate of
bisphenol AF, the diacetate of sulfonyl diphenol, and the diacetate
of hydroquinone.
[0055] When cured with polyhydroxy compounds, the curable
compositions will also generally include a cure accelerator. The
most useful accelerators are quaternary phosphonium salts,
quaternary alkylammonium salts, or tertiary sulfonium salts.
Particularly preferred accelerators are n-tetrabutylammonium
hydrogen sulfate, tributylallylphosphonium chloride and
benzyltriphenylphosphonium chloride. Other useful accelerators
include those described in U.S. Pat. Nos. 5,591,804; 4,912,171;
4,882,390; 4,259,463 and 4,250,278 such as tributylbenzylammonium
chloride, tetrabutylammonium bromide, tetrabutylammonium chloride,
benzyl tris(dimethylamino)phosphonium chloride;
8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenonium chloride,
[(C.sub.6H.sub.5).sub.2S.sup.+(C.sub.6H.sub.13)][Cl].sup.-, and
[(C.sub.6H.sub.13).sub.2S(C.sub.6H.sub.5)].sup.+[CH.sub.3CO.sub.2].sup.-.
In general, about 0.2 phr accelerator is an effective amount, and
preferably about 0.35-1.5 phr is used.
[0056] If quaternary ammonium or phosphonium salts of bisphenols
are used as curing agents, then addition of a cure accelerator is
not necessary.
[0057] The polyhydroxy cure system will also contain a metal
compound composed of a divalent metal oxide, such as magnesium
oxide, zinc oxide, calcium oxide, or lead oxide, or a divalent
metal hydroxide; or a mixture of the oxide and/or hydroxide with a
metal salt of a weak acid, for example a mixture containing about
1-70 percent by weight of the metal salt. Among the useful metal
salts of weak acids are barium, sodium, potassium, lead, and
calcium stearates, benzoates, carbonates, oxalates, and phosphites.
The amount of the metal compound added is generally about 1-15 phr,
about 2-10 parts being preferred.
[0058] Other additives may be compounded into the fluoroelastomer
to optimize various physical properties. Such additives include
carbon black, stabilizers, plasticizers, lubricants, pigments,
fillers, and processing aids typically utilized in
perfluoroelastomer compounding. Any of these additives can be
incorporated into the compositions of the present invention,
provided the additive has adequate stability for the intended
service conditions.
[0059] Carbon black is used in elastomers as a means to balance
modulus, tensile strength, elongation, hardness, abrasion
resistance, conductivity, and processability of the compositions.
Carbon black is generally useful in amounts of from 5-60 phr.
[0060] In addition, or in the alternative, fluoropolymer fillers
may be present in the composition. Generally from 1 to 50 phr of a
fluoropolymer filler is used, and preferably at least about 5 phr
is present. The fluoropolymer filler can be any finely divided,
easily dispersed plastic fluoropolymer that is solid at the highest
temperature utilized in fabrication and curing of the
perfluoroelastomer composition. By solid, it is meant that the
fluoroplastic, if partially crystalline, will have a crystalline
melting temperature above the processing temperature(s) of the
perfluoroelastomer(s). Such finely divided, easily dispersed
fluoroplastics are commonly called micropowders or fluoroadditives.
Micropowders are ordinarily partially crystalline polymers.
[0061] A preferred additive class includes molecular sieves,
particularly zeolites. Molecular sieve zeolites are crystalline
aluminosilicates of Group IA and Group IIA elements, such as
sodium, potassium, magnesium, and calcium. Chemically, they are
represented by the empirical formula:
M.sub.2/nO.Al.sub.2O.sub.3.ySiO.sub.2.wH.sub.2O where y is 2 or
greater, n is the cation valence, and w represents the water
contained in the voids of the zeolite. Commercially available
examples of such compositions include Molecular Sieve 3A, Molecular
Sieve 4A, Molecular Sieve 5A, and Molecular Sieve 13X, all
available from Aldrich Chemical Co., Inc. Milwaukee, Wis. Use of
this class of additives prevents sponging and improves heat aging
of vulcanizates upon press curing in many instances. In general,
use of about 1-5 phr is sufficient.
[0062] Other preferred additives include modified silane coated
mineral fillers. By "modified silane" is meant that the silane
contains at least one reactive functional group such as an amino
group, or an epoxy group. The mineral fillers used in this
invention are preferably somewhat alkaline, such as calcium
metasilicates (CaSiO.sub.3), especially wollastonite. Wollastonite
coated with either an aminosilane or an epoxysilane is especially
preferred. These compounds are commercially available from
Quarzwerke GmbH of Freschen, Germany as Tremin.RTM.283 EST
(epoxysilane treated wollastonite) and Tremin.RTM.283 AST
(aminosilane treated wollastonite). These modified silane coated
mineral fillers prevent sponging of the fluoroelastomer composition
during press cure and also accelerate the cure rate. Generally,
about 5 to 80 phr modified silane coated mineral filler is useful
in the compositions of this invention, about 10 to 60 phr being
preferred.
[0063] The crosslinking agent, accelerator, metal oxide, and other
additives are generally incorporated into the polymer by means of
an internal mixer or on a rubber mill. The resultant composition is
then cured, generally by means of heat and pressure, for example by
compression transfer or injection molding.
[0064] The curable compositions of the present invention are useful
in production of gaskets, tubing, seals and other molded
components. Such articles are generally produced by molding a
compounded formulation of the curable composition with various
additives under pressure, curing the part, and then subjecting it
to a post cure cycle. Depending on the monomers employed in the
fluoroelastomer, the cured compositions have excellent low
temperature flexibility and processability as well as excellent
thermal stability and chemical resistance. They are particularly
useful in applications such as seals and gaskets requiring a good
combination of oil resistance, fuel resistance and low temperature
flexibility, for example in fuel injection systems, fuel line
connector systems and in other seals for high and low temperature
automotive uses.
[0065] The invention is now illustrated by certain embodiments
wherein all parts and percentages are by weight unless otherwise
specified.
EXAMPLES
TEST METHODS
[0066] Cure Characteristics
[0067] Unless otherwise noted, cure characteristics were measured
using an Alpha Technologies Ltd. 2000E moving disk rheometer (MDR),
under conditions corresponding to ISO 6502 at a moving die
frequency of 1.66 Hz, oscillation amplitude of.+-.0.5.degree.,
temperature of 180.degree. C., sample size of 7-8 g, and the
duration of the test was 12 minutes. The following cure parameters
were recorded:
[0068] M.sub.H: maximum torque level, in units of dN.multidot.m
[0069] M.sub.L: minimum torque level, in units of dN.multidot.m
[0070] Delta M: difference between maximum and minimum torque, in
units of dN.multidot.m
[0071] t.sub.s2: minutes to a 2.26 dNm rise above M.sub.L
[0072] tc50: minutes to 50% of maximum torque
[0073] tc90: minutes to 90% of maximum torque
Example 1
[0074] A monomer of the invention,
9,9,12-trihydro-perfluoro(3,6,10-trioxa- -5-methyl-1-tridecene)
[CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)O--CF.sub.-
2CF.sub.2--CH.sub.2O--CF.sub.2CFHCF.sub.3], was prepared by the
following three step process.
[0075] In the first step, the chlorinated hydroxy ether
intermediate
1,2-dichloro-9,9-dihydro-9-hydroxy-perfluoro(3,6-dioxa-5-methyl-nonane)
[CF.sub.2Cl--CFCl--O--CF.sub.2CF(CF.sub.3)O--CF.sub.2CF.sub.2--CH.sub.2OH-
] was prepared by chlorinating the hydroxy vinyl ether
9,9-dihydro-9-hydroxy-perfluoro(3,6-dioxa-5-methyl-1-nonene)
[CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)O--CF.sub.2CF.sub.2--CH.sub.2OH]-
. The preparation of this hydroxy vinyl ether is disclosed in U.S.
Pat. No. 4,982,009. In this first step, 300 g (0.761 moles) of the
hydroxy vinyl ether was cooled to a temperature between 0 and
10.degree. C. and then chlorinated with neat chlorine. The progress
of the reaction was monitored by gas chromatography. Chlorination
was terminated when the majority of the hydroxy vinyl ether had
been consumed. The resulting chlorinated hydroxy ether was purified
by distillation, resulting in 200 g of a clear, colorless liquid
having a boiling point of 100.degree. C. at 25 mm Hg. NMR was used
to positively identify the product: .sup.1H-NMR (400 MHz,
CDCl.sub.3): .delta.4.00 (t, J=13.8 Hz, 2H), 1.94 (s, br, 1H); and
.sup.19F-NMR: (376.89 MHz, CDCl.sub.3): -71.3 (m, 2F), -77.4 (m,
1F), -80.2 (t, 3F), -83.8 to -86.0 (m, 4F), -126.5 (t, 2F), -146.0
(m, 1F).
[0076] In the second step of the synthesis, the chlorinated hydroxy
ether prepared in step 1 above, was condensed with
hexafluoropropene to produce the chlorinated ether intermediate
1,2-dichloro-9,9,12-trihydro-perfluoro-
(3,6,10-trioxa-5-methyl-tridecane
[CF.sub.2Cl--CFCl--O--CF.sub.2CF(CF.sub.-
3)O--CF.sub.2CF.sub.2--CH.sub.2O--CF.sub.2CFHCF.sub.3]. This was
accomplished by charging a 400 ml stainless steel shaker tube with
the
1,2-dichloro-9,9-dihydro-9-hydroxy-perfluoro-(3,6-dioxa-5-methyl-octane)
(46.5 g, 0.1 mol) which was produced in step 1, potassium
t-butoxide (1.58 g, 0.015 mol) and anhydrous dimethyl sulfoxide
solvent (25 ml). The tube was then sealed, cooled and evacuated.
Next, hexafluoropropene (30 g, 0.20 mol) was transferred into the
tube. The tube was agitated for 8 hrs at 45.degree. C. After
cooling, the tube contents was distilled to give 45 g of
1,2-dichloro-9,9,12-trihydro-perfluoro(3,6,10-trioxa-5-methy-
ltridecane) as a clear, colorless liquid, having a boiling point of
99-100.degree. C. at 27-28 mm Hg. Product identity was confirmed by
NMR: .sup.1H-NMR (400 MHz, CDCl.sub.3): .delta.4.85 (dm, J=50 Hz,
2H), 4.35 (t, J=11.8 Hz, 1H); .sup.19F-NMR: (376.89 MHz,
CDCl.sub.3): -71.4 (m, 2F), -77.4 (m, 1F), -76.0 (m, 3F), -80.3 (m,
3F), -80.5 to -85.0 (m, 6F), -124.1 (m, 2F), -145.9 (m, 1F), -212.5
(m, 1F).
[0077] In the third step, the chlorinated ether intermediate
produced in the second step was reduced to yield the fluorovinyl
ether monomer of this invention. In this step, a reaction flask was
charged with zinc-dust (23.5 g, 0.359 mol) in anhydrous
dimethylformamide (DMF) solvent (180 ml). Bromine (1.5 ml) was then
added to the flask in order to activate the zinc metal. The
1,2-dichloro-9,9,12-trihydro-perfluoro-(3,6,10-trioxa-
-5-methyl-1-tridecene (87 g, 0.141 mol) (produced above in the
second step) was added and the reaction mixture was heated to a
temperature between 98 and 104.degree. C. for 4 hours. Gas
chromatography indicated that the chlorinated ether reactant was
completely consumed. The reaction mixture was cooled and filtered
to remove the zinc metal and zinc halide residues. The resulting
two-layer liquid was separated, and the bottom layer was washed
with water and distilled to give 42 g of the
9,9,12-trihydro-perfluoro-(3,6,10-trioxa-5-methyl-1-tridecene)
monomer of this invention. The monomer was a clear, colorless
liquid, having a boiling point of 88-89.degree. C. at 41-42 mm Hg.
This product was a diastereomer mixture. NMR confirmed the identity
of the product: .sup.1H-NMR (400 MHz, CDCl.sub.3): [.delta.4.84
(dm, J=43.8 Hz, major isomer), 4.47 (dm, minor isomer), 1H total],
4.35 (t, J=11.7 Hz, 2H); .sup.19F-NMR: (376.89 MHz, CDCl.sub.3):
[-76.0 (m, major isomer), -68.2 (m, minor isomer), 3F total], -80.4
(m, 3F), -82.2 to -85.8 (m, 6F), -113.6 (m, 1F), -122.1 (4m, 1F),
[-123.9 (m, major isomer), -124.2 (m, minor isomer), 2F total],
-135.9 (4m, 1F), -145.5 (m, 1F), [-181.7 (m), -188.6 (dm), -212.5
(m), 1F total]. IR (neat): 1840 cm.sup.-1 (CF.sub.2.dbd.CFO--).
Example 2
[0078] Fluoroelastomer polymer A of this invention (containing
copolymerized units of
VF.sub.2/PMVE/TFE/CF.sub.2.dbd.CF--O--CF.sub.2CF(C-
F.sub.3)O--CF.sub.2CF.sub.2--CH.sub.2O--CF.sub.2CFHCF.sub.3) was
prepared in the following manner.
[0079] A 4-liter polymerization vessel was charged with de-ionized
water (2000 ml), disodium phosphate heptahydrate (20 g), ammonium
perfluorooctanoate (3.9 g), and
9,9,12-trihydro-perfluoro(3,6,10-trioxa-5- -methyl-1-tridecene)
[CF.sub.2.dbd.CF--O--CF.sub.2CF(CF.sub.3)O--CF.sub.2C-
F.sub.2--CH.sub.2O--CF.sub.2CFHCF.sub.3] monomer (36 g). The
reactor was sealed. Oxygen was removed from the reactor by
evacuating it and then purging with nitrogen gas. The latter
process was repeated three times. The reactor was then charged with
a monomer gas mixture of TFE (10 g/hr), VF.sub.2 (320 g/hr) and
PMVE (670 g/hr) until the pressure had reached 200 psi (1.38 MPa)
at 80.degree. C. The reactor contents were stirred by a mechanical
stirrer operating at 200 rpm. A solution of ammonium persulfate
initiator (2.0 wt. % in water, 30 ml) was then added to the reactor
at a rate of 10 ml/min. When a pressure drop (due to monomer
consumption during the polymerization) was observed, the monomer
gas feed was switched to a mixture of TFE (37 g/hr), VF.sub.2 (212
g/hr) and PMVE (140 g/hr). The monomer feed flow rate was
controlled so as to maintain the total reactor vessel pressure at
200 psi (1.38 MPa) as additional ammonium persulfate initiator
solution was co-fed to the reactor at a rate of 0.2 ml/min. The
polymerization was terminated after a total of 728 grams of monomer
had been fed to the reactor. The resulting fluoroelastomer latex
was then coagulated by addition of a magnesium sulfate aqueous
solution. The coagulated fluoroelastomer polymer was collected by
filtration, and washed thoroughly with warm water (70 .degree. C.).
Polymer was then dried in an air oven at 80.degree. C. The
resulting fluoroelastomer polymer had a T.sub.g of -30.5.degree.
C., as determined by Differential Scanning Calorimetry (DSC). The
composition of the polymer was analyzed by infrared spectroscopy
and .sup.19F-NMR (in hexafluorobenzene at 80.degree. C.) and was
determined to be 75.17 mol % VF.sub.2, 6.30 mol % TFE, 18.44 mol %
PMVE and 0.087 mol %
9,9,12-trihydro-perfluoro(3,6,10-trioxa-5-methyl-1-tridecene).
These mol % values correspond to 56.27 wt. %, 7.37 wt. %, 35.80 wt.
% and 0.55 wt. %, respectively.
Example 3
[0080] Samples of polymer A from Example 2, and of a control
polymer (a fluoroelastomer of the prior art containing 33.3 wt. %
VF.sub.2, 39.4 wt. % PMVE and 27.3 wt. % TFE) were compounded on a
two-roll rubber mill with the components shown in Table I. Cure
characteristics, measured according to the Test Method described
above, are also reported in Table I.
[0081] The control polymer, which contained no cure site monomer,
exhibited essentially no cure response, whereas polymer A of this
invention cured well.
1 TABLE I Formulation Sample 1 Control Polymer A 100 Control
Polymer 100 Tremin .RTM. 283 600EST.sup.1 45 MT Carbon Black.sup.2
2.5 10 Calcium Hydroxide.sup.3 6 2 MgO.sup.4 3 2 VPA No. 2.sup.5 1
TBAHS.sup.6 0.5 1 Bisphenol AF.sup.7 2 2 Cure Characteristics
M.sub.L, dNm 10.19 -- M.sub.H, dNm 29.32 -- Delta M, dNm 19.13 0.6
t.sub.s2, minutes 2.2 -- tc50, minutes 3.3 -- tc90, minutes 6.2 --
.sup.1Calcium meta-silicate treated with aminosilane (available
from Quarzwerke GmbH, Freschen, Germany) .sup.2Thermax FF N 990
medium thermal carbon black (available from Lehmann & Voss Co.)
.sup.3Rhenofit CF (available from Bayer) .sup.4Elastomag .RTM. 170
(available from Morton Performance Chemicals, Inc.) .sup.5Rice Bran
Wax (available from DuPont Dow Elastomers L.L.C.)
.sup.6Tetrabutylammonium hydrogen sulfate (available from DuPont
Dow Elastomers L.L.C.)
.sup.74,4'-(Hexafluoroisopropylidene)diphenol (available from
DuPont Dow Elastomers L.L.C.)
* * * * *