U.S. patent application number 10/473699 was filed with the patent office on 2005-05-12 for process for crosslinking of acrylic ester copolymers.
Invention is credited to Cohen, Gordon Mark, Deyrup, Edward Johnson, Harrell, Jerald Rice.
Application Number | 20050101742 10/473699 |
Document ID | / |
Family ID | 23088660 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050101742 |
Kind Code |
A1 |
Cohen, Gordon Mark ; et
al. |
May 12, 2005 |
Process for crosslinking of acrylic ester copolymers
Abstract
Disclosed is a process for crosslinking copolymers of acrylic
esters by converting some of the ester groups to ester or amide
groups which contain unsaturation, and then sulfur or peroxide
curing the resulting polymers. The resulting crosslinked polymers
often have excellent vulcanizate properties, and are useful
especially in elastomeric form as seals and gasket.
Inventors: |
Cohen, Gordon Mark;
(Wynnewood, PA) ; Deyrup, Edward Johnson;
(Wilmington, DE) ; Harrell, Jerald Rice;
(Wilmington, DE) |
Correspondence
Address: |
Barbara C Siegell
E I Du Pont De Nemours and Company
Legal-Patents
Wilmington
DE
19898
US
|
Family ID: |
23088660 |
Appl. No.: |
10/473699 |
Filed: |
September 29, 2003 |
PCT Filed: |
April 16, 2002 |
PCT NO: |
PCT/US02/12671 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60284048 |
Apr 16, 2001 |
|
|
|
Current U.S.
Class: |
525/282 |
Current CPC
Class: |
C08F 2810/20 20130101;
C08F 8/14 20130101; C08L 33/00 20130101; C08F 2810/30 20130101;
C08F 8/06 20130101; C08F 8/14 20130101; C08F 120/18 20130101; C08F
8/34 20130101; C08F 8/14 20130101; C08F 120/18 20130101; C08F 8/14
20130101; C08F 120/18 20130101 |
Class at
Publication: |
525/282 |
International
Class: |
C08F 265/10 |
Claims
What is claimed is:
1. A process for crosslinking a polymer, comprising: (a)
transesterifying or amidating a first polymer consisting
essentially of about 60 or more mole percent of 4and up to about 40
mole percent of one or more comonomers selected from the group
consisting of aromatic hydrocarbon olefins, acrylonitrile, olefinic
monomers containing one or more functional groups selected from the
group consisting of chlorine, epoxy, and carboxylic acid, and
cyanoalkyl acrylates wherein alkyl comprises 2-8 carbons, with an
alcohol or a primary amine which contains one or more olefinic
bonds, to form a second polymer having side chains containing said
olefinic bonds; and (b) crosslinking said second polymer using a
sulfur or peroxide cure system; and wherein: R.sup.1 is methyl or
hydrogen; and R.sup.2 is hydrocarbyl, substituted hydrocarbyl, or a
mixture thereof.
2. The process as recited in claim 1 wherein said first polymer is
an elastomer.
3. The process as recited in claim 2 wherein each R.sup.2 is
independently alkyl containing 1-8 carbon atoms optionally
substituted by one or more ether oxygens.
4. The process as recited in claim 3 wherein R.sup.1 is hydrogen
and each R.sup.2 is independently selected from the group
consisting of ethyl, butyl, methoxyethyl, ethoxyethyl, and mixtures
thereof, with the proviso that at least 50 mol % of the R.sup.2
groups must be ethyl, butyl, or a combination thereof.
5. The process as recited in claim 1 wherein said comonomer is
acrylonitrile.
6. The process as recited in claims 1, 2, 4 or 5 wherein a
transesterification is carried out.
7. The process as recited in claim 6 wherein a transesterification
catalyst is present.
8. The process as recited in claim 7 wherein said catalyst is a
tetraalkyl titanate or a tin compound.
9. The process as recited in claim 6 wherein said alcohol has the
formula HR.sup.3(CR.sup.4.dbd.CR.sup.5R.sup.6).sub.tCH.sub.2OH
wherein R.sup.3 and each R.sup.5 are each independently a covalent
bond, alkylene or alkylidene, and R.sup.4 and R.sup.6 are each
independently hydrogen or alkyl, and t is 1, 2 or 3.
10. The process as recited in claim 6 wherein said alcohol is one
or more of oleyl, linoleyl or linolenyl alcohols.
11. The process as recited in claim 1 wherein during (b) said first
polymer is also present, provided that said second polymer is at
least 20% by weight of the total of said first polymer and said
second polymer.
12. A composition comprising: (a) a second polymer made by
transesterifying or amidating a first polymer consisting
essentially of about 60 or more mole percent of 5and up to about 40
mole percent of one or more comonomers selected from the group
consisting of aromatic hydrocarbon olefins, acrylonitrile, olefinic
monomers containing one or more functional groups selected from the
group consisting of chlorine, epoxy, and carboxylic acid, and
cyanoalkyl acrylates wherein alkyl comprises 2-8 carbons, with an
alcohol or a primary amine which contains one or more olefinic
bonds; and (b) a sulfur or peroxide cure system; and wherein:
R.sup.1 is methyl or hydrogen; and R.sup.2 is hydrocarbyl and/or
substituted hydrocarbyl.
13. The composition as recited in claim 12 wherein said first
polymer is an elastomer.
14. The composition as recited in claim 13 wherein each R.sup.2 is
independently alkyl containing 1-8 carbon atoms optionally
substituted by one or more ether oxygens.
15. The composition as recited in claim 14 wherein R.sup.1 is
hydrogen and each R.sup.2 is independently selected from the group
consisting of ethyl, butyl, methoxyethyl, ethoxyethyl, and mixtures
thereof, with the proviso that at least 50 mol % of the R.sup.2
groups must be ethyl, butyl, or a combination thereof.
16. The composition as recited in claim 13 wherein said comonomer
is acrylonitrile.
17. The composition as recited in claim 12 further comprising up to
80% by weight of a polymer consisting essentially of at least 60
mole percent of 6and up to about 40 mole percent of one or more
comonomers selected from the group consisting of aromatic
hydrocarbon olefins, acrylonitrile, olefinic monomers containing
one or more functional groups selected from the group consisting of
chlorine, epoxy, and carboxylic acid, and cyanoalkyl acrylates
wherein alkyl comprises 2-8 carbons, and wherein R.sup.1 is methyl
or hydrogen; and R.sup.2 is hydrocarbyl, substituted hydrocarbyl,
or a mixture thereof.
18. A composition comprising: (a) a polymer consisting essentially
of at least 60 mole percent of 7and up to about 40 mole percent of
one or more comonomers selected from the group consisting of
aromatic hydrocarbon olefins, acrylonitrile, olefinic monomers
containing one or more functional groups selected from the group
consisting of chlorine, epoxy, and carboxylic acid, and cyanoalkyl
acrylates wherein alkyl comprises 2-8 carbons; and (b) a sulfur or
peroxide cure system; wherein: R.sup.1 is methyl or hydrogen; and
R.sup.2 is hydrocarbyl, substituted hydrocarbyl, or a mixture
thereof, provided that at least 0.5 mole percent of R.sup.2
contains olefinic unsaturation.
19. The composition as recited in claim 18 wherein said polymer is
an elastomer.
20. The composition as recited in claim 19 wherein each R.sup.2
which does not contain olefinic unsaturation is independently alkyl
containing 1-8 carbon atoms optionally substituted by one or more
ether oxygens.
21. The composition as recited in claim 20 wherein R.sup.1 is
hydrogen and R.sup.2 which does not contain unsaturation is
selected from the group consisting of ethyl, butyl, methoxyethyl,
ethoxyethyl, and mixtures thereof.
22. The composition as recited in claim 19 wherein said polymer
consists essentially of 100 mol % of (I).
23. The composition as recited in claim 18 further comprising up to
80% by weight of a polymer consisting essentially of about 60 or
more mole percent of 8and up to about 40 mole percent of one or
more comonomers selected from the group consisting of aromatic
hydrocarbon olefins, acrylonitrile, olefinic monomers containing
one or more functional groups selected from the group consisting of
chlorine, epoxy, and carboxylic acid, and cyanoalkyl acrylates
wherein alkyl comprises 2-8 carbons, and wherein R.sup.1 is methyl
or hydrogen; and R.sup.2 is hydrocarbyl, substituted hydrocarbyl,
or a mixture thereof; provided that none of R.sup.2 contains
olefinic unsaturation.
24. The process as recited in claim 1 or 6 wherein said first
polymer is dried before step (a).
25. The product of the process of claim 1, 6 or 7.
Description
FIELD OF THE INVENTION
[0001] Copolymers of acrylic esters are crosslinked by converting
some of the ester groups to ester or amide groups which contain
unsaturation and then sulfur or peroxide curing the resulting
polymers.
TECHNICAL BACKGROUND
[0002] Crosslinking (also sometimes termed vulcanization or curing)
of polymers yields products which often have improved properties
for their intended uses. This is particularly true when the polymer
is an elastomer, and curing of elastomers is very commonly done,
for instance using sulfur or peroxide curing. For sulfur cures,
generally speaking the polymer contains olefinic unsaturation,
while for peroxide curing the presence of olefinic unsaturation is
often preferable, see for instance H. Mark, et al., Ed.,
Encyclopedia of Polymer Science and Engineering, Vol. 17,
McGraw-Hill Book Co., New York, 1989, p. 666-698.
[0003] However, some types of elastomers do not contain olefinic
unsaturation, and so are not generally sulfur cured, and/or cured
by peroxides with some difficulty. These elastomers are cured using
other curing systems. For example, elastomeric ethylene/acrylic
copolymers may be crosslinked by the use of primary diamines, which
form crosslinks, see for instance H. Mark, et al., Ed.,
Encyclopedia of Polymer Science and Engineering, Vol. 1,
McGraw-Hill Book Co., New York, 1985, p. 325-334. In order to aid
in such crosslinking to more readily form crosslinks and/or form
more stable crosslinks curesite monomers, such as carboxylic acids
or half acid esters may be copolymerized into the polymer, see for
instance U.S. Pat. Nos. 3,883,472 and 3,904,588. In another
example, polyacrylate elastomers are typically crosslinked through
curesites containing chlorine, epoxy, and/or carboxylic acid
groups. These curesites may be obtained from curesite monomers
which are copolymerized into the polymer, for example,
2-chloroethyl vinyl ether, vinyl chloroacetate, p-vinylbenzyl
chloride, or glycidyl acrylate, see for instance Kirk-Othmer
Encyclopedia of Chemical Technology, 4th edition, Vol. 8, John
Wiley and Sons, New York, 1993 p. 927 and Polymeric Materials
Encyclopedia, Vol. 1, CRC Press, New York, 1996, p. 74.
[0004] However, it is often desirable to crosslink such polymers
using conventional sulfur or peroxide curing systems such as are
widely employed in the art, because such cures are already in use
in many factories for a wide variety of common elastomers, and/or
the curing agents are less expensive and/or less toxic. In order to
make such types of polymers curable with those peroxide or sulfur
cure systems, it is desirable to introduce into them olefinic
unsaturation containing groups. These groups should be introduced
in such a way so as not to harm the basic polymer properties, so
that the polymers may be readily and/or economically cured, and/or
the resulting crosslinks ate stable, so as to give good vulcanizate
properties.
[0005] In order to form polyacrylate elastomers it is known to
introduce olefinic unsaturation by copolymerization with comonomers
such as butadiene, isoprene, allyl maleate, dicyclopentenyl
acrylate, 5-ethylidene-2-norbornene, or tetrahydrobenzyl acrylate.
These monomers are expensive and in some cases may cause the
polymer to prematurely crosslink in the polymerization reaction,
see for instance Kirk-Othmer Encyclopedia of Chemical Technology,
4th edition, Vol. 8, John Wiley and Sons, New York, 1993, p.
928.
[0006] It is also possible to introduce olefinic unsaturation
containing groups by chemical modification of the polymer after the
polymerization. Japanese Patent Application 62-121746 describes the
esterification of a polymer made from ethylene, an acrylic ester
and maleic anhydride and/or a maleic half acid ester which is
"modified" with an olefinically unsaturated amine or alcohol, and
then cured using a sulfur or peroxide cure. No mention is made of
polymers containing only ethylene and acrylic ester repeat
units.
[0007] German Patent Application 3,715,027 A1 describes various
copolymers of ethylene and acrylic acids and/or esters, and
optionally other monomers such as maleic anhydride, their reaction
with olefinic alcohols, including those with polyunsaturation, and
their subsequent crosslinking by oxidation, e.g., reaction with
air, often in the presence of an oxidation catalyst. The polymers
are useful as thermosetting melt adhesives. No mention is made of
sulfur or peroxide curing. U.S. Pat. No. 5,736,616 is similar to
German Patent Application 3,715,027, in that a polymer containing
pendant unsaturation is used as an oxygen scavenger (react with
oxygen). The polymer is made by polymerizing ethylene and acrylic
esters and/or acids and then esterifying or transesterifying the
resulting polymer with an unsaturated alcohol. No mention is made
of curing such a polymer using a sulfur or peroxide cure.
[0008] U.S. Pat. No. 5,093,429 describes the preparation of a
polymer containing olefinic unsaturation by direct copolymerization
of ethylene, an acrylic ester, and a copolymerizable monomer
containing unsaturation which survives the polymerization (for
example has a copolymerizable double bond and a double bond which
is unreactive in the polymerization), or by copolymerization of
ethylene, and acrylic ester, and another copolymerizable monomer
which may then be reacted with an unsaturated alcohol or amine to
attach such unsaturation to the polymer. The polymer containing
unsaturation may then be crosslinked using a sulfur or peroxide
curing system. No mention is made of using the acrylic ester as a
site to attach the olefinic unsaturation.
[0009] In some instances the crosslinks that result from curesite
monomers present in some of the above references are not as stable
as desired because linkages between the crosslinkable groups (e.g.,
olefinic unsaturation) are not as stable as desired. U.S. Pat. No.
4,399,263, for example, mentions that at temperatures above
160.degree. C. ethylene/alkyl acrylate/maleic acid ester polymers
form anhydride moieties by internal reaction at the acid-ester
curesite. The crosslinks may not be sufficiently stable because the
curesite monomers and/or polymer-modifying reagents, which attach
curable functionalities onto the polymer, introduce groups into the
composition which catalyze unwanted reactions.
SUMMARY OF THE INVENTION
[0010] This invention concerns a process for crosslinking a
polymer, comprising:
[0011] (a) transesterifying or amidating a first polymer consisting
essentially of about 60 or more mole percent of 1
[0012] and up to about 40 mole percent of one or more comonomers
selected from the group consisting of aromatic hydrocarbon olefins,
acrylonitrile, olefinic monomers containing one or more functional
groups selected from the group consisting of chlorine, epoxy, and
carboxylic acid, and cyanoalkyl acrylates wherein alkyl comprises
2-8 carbons, with an alcohol or a primary amine which contains one
or more olefinic bonds, to form a second polymer having side chains
containing said olefinic bonds; and
[0013] (b) crosslinking said second polymer using a sulfur or
peroxide cure system;
[0014] and wherein:
[0015] R.sup.1 is methyl or hydrogen; and
[0016] R.sup.2 is hydrocarbyl, substituted hydrocarbyl, or a
mixture thereof.
[0017] Also disclosed herein is a composition comprising:
[0018] (a) a second polymer made by transesterifying or amidating a
first polymer consisting essentially of about 60 or more mole
percent of 2
[0019] and up to about 40 mole percent of one or more comonomers
selected from the group consisting of aromatic hydrocarbon olefins,
acrylonitrile, olefinic monomers containing one or more functional
groups selected from the group consisting of chlorine, epoxy, and
carboxylic acid, and cyanoalkyl acrylates wherein alkyl comprises
2-8 carbons, with an alcohol or a primary amine which contains one
or more olefinic bonds; and
[0020] (b) a sulfur or peroxide cure system;
[0021] and wherein:
[0022] R.sup.1 is methyl or hydrogen; and
[0023] R.sup.2 is hydrocarbyl, substituted hydrocarbyl, or a
mixture thereof.
[0024] Another composition disclosed herein comprises:
[0025] (a) a polymer consisting essentially of about 60 or more
mole percent of 3
[0026] and up to about 40 mole percent of one or more comonomers
selected from the group consisting of aromatic hydrocarbon olefins,
acrylonitrile, olefinic monomers containing one or more functional
groups selected from the group consisting of chlorine, epoxy, and
carboxylic acid, and cyanoalkyl acrylates wherein alkyl comprises
2-8 carbons; and
[0027] (b) a sulfur or peroxide cure system;
[0028] and wherein:
[0029] R.sup.1 is methyl or hydrogen; and
[0030] R.sup.2 is hydrocarbyl, substituted hydrocarbyl, or a
mixture thereof provided that at least 0.5 mole percent of R.sup.2
contains olefinic unsaturation.
DETAILS OF THE INVENTION
[0031] Herein certain terms are used, and they are defined
below.
[0032] By hydrocarbyl is meant a univalent radical containing only
carbon and hydrogen. Unless otherwise specified it is preferred
that it contain 1 to 30 carbon atoms.
[0033] By substituted hydrocarbyl is meant hydrocarbyl containing
one or more substituents (functional groups) which do not interfere
with (as appropriate) amidation, transesterification and
crosslinking. Useful substituents include oxo (keto), halo, ether
and thioether. Unless otherwise specified it is preferred that it
contain 1 to 30 carbon atoms.
[0034] By a hydrocarbon olefin is meant a polymerizable olefin
containing only carbon and hydrogen.
[0035] By olefinic double bond is meant a carbon-carbon double bond
which is not part of an aromatic ring. Preferably the olefinic
double bond has one or more allylic hydrogen atoms, particularly
when a peroxide cure is used.
[0036] By an acrylic ester is meant a compound of formula (I).
[0037] By a dipolymer is meant a copolymer containing repeat units
derived from two monomers.
[0038] By a conventional sulfur cure system is meant any of the
conventional known cure systems that cure unsaturated polymers
using sulfur chemistry, see for instance H. Mark, et al.,
Encyclopedia of Polymer Science and Engineering, Vol. 17,
McGraw-Hill Book Co., New York, 1989, p. 666-698, and W. Hoffmann,
Vulcanization and Vulcanizing Agents, MacLaren & Sons, Ltd.,
London, 1967, both of which are hereby included by reference. The
cure system may include conventional accelerators and other
compounds, and may or may not have free sulfur present.
[0039] By a peroxide cure system is meant any of the conventional
known cure systems that cure unsaturated polymers (they may also
cure polymers containing no unsaturation) using organic peroxides,
see for instance W. Hoffmann, Vulcanization and Vulcanizing Agents,
MacLaren & Sons, Ltd., London, 1967, which is hereby included
by reference. Besides the peroxide being present, other
conventional ingredients such as so-called coagents may also be
present.
[0040] By elastomeric or an elastomer is meant that the heat of
fusion of any polymer crystallites present with a melting point
(Tm) of 50.degree. C. or more is less than 5 J/g, more preferably
less than about 2 J/g, and preferably no polymeric crystallites are
present at 25.degree. C., and that the glass transition temperature
(Tg) of the polymer is less than about 50.degree. C., more
preferably less than about 20.degree. C., and especially preferably
less than about 0.degree. C. The Tm and heat of fusion of the
polymer are determined by ASTM method D3451 at a heating rate of
10.degree. C./min and the Tm is taken as the peak of the melting
endotherm, while the Tg of the polymer is determined using ASTM
Method E1356 at a heating rate of 10.degree. C./min, taking the
midpoint temperature as the Tg. Both of these are determined on a
second heating of the polymer.
[0041] The first polymer of the present invention consists
essentially of acrylate monomer units according to formula (I), and
up to 40 mol-% of non-acrylate monomer units. In (I), preferably,
R.sup.1 is hydrogen, and R.sup.2 is hydrocarbyl, more preferably,
alkyl containing 1 to 8 carbon atoms optionally substituted by
ether oxygen. It will be understood by one of skill in the art that
the acrylate moiety of the first polymer may be a mixture of
acrylate monomers; that is, not all the R.sup.2 groups in the
polymer need be the same. In a preferred embodiment, the R.sup.2
groups are ethyl or butyl, or a combination of the two. It is
well-known in the art to employ up to about 50 mol % of additional
acrylate monomers in combination with ethyl or butyl acrylate, to
effect one or another desired modification to the properties of the
resultant polymer. Preferred additional acrylate monomers include
methoxy ethyl acrylate, ethoxy ethyl acrylate, and mixtures
thereof. Also preferably the first polymer is elastomeric.
[0042] The first polymer of the invention may further be a
copolymer of one or more acrylate monomers with up to 40 mol % of
non-acrylate monomers selected from the group consisting of
aromatic hydrocarbon olefins, acrylonitrile, olefinic curesite
monomers containing chlorine, epoxy, or carboxylic acid groups, and
cyanoalkyl acrylates wherein alkyl comprises 2-8 carbons.
Acrylonitrile is a preferred non-acrylate comonomer.
[0043] Useful monomers that contain chlorine, epoxy, or carboxylic
acid groups include 2-chloroethyl vinyl ether, vinyl chloroacetate,
p-vinylbenzyl chloride, acrylic acid, methacrylic acid, allyl
glycidyl ether, glycidyl acrylate, and glycidyl methacrylate.
Useful aromatic hydrocarbon olefins include styrene,
.alpha.-methylstyrene, and substituted styrenes.
[0044] Useful alcohols which contain olefinic bonds include
alcohols of the formula
H(CH.sub.2).sub.pCH.dbd.CH(CH.sub.2).sub.qCH.sub.2OH, (II), wherein
p is 0 or an integer of 1 to 10, and q is 0 or an integer of 1 to
30, HR.sup.3(CR.sup.4.dbd.CR.sup.5R.sup.6).sub.tCl.sub.2OH (III)
wherein R.sup.3 and each R.sup.5 are each independently a covalent
bond, alkylene or alkylidene, and R.sup.4 and R.sup.6 are each
independently hydrogen or alkyl, wherein R.sup.3, R.sup.4, R.sup.5
and R.sup.6 each independently contain 1 to 20 carbon atoms, and t
is 1, 2 or 3. (II) is a preferred alcohol, and in (II) it is
preferred that p is 0 and/or q is 5 to 17, or p is 8 and q is 7. It
is preferred that these alcohols be primary or secondary alcohols,
and more preferred that they be primary alcohols. Mixtures of
alcohols may be used, for example a mixture of oleyl, linoleyl and
linolenyl alcohols. Specific preferred alcohols include
10-undecen-1-ol, oleyl alcohol, cis-3,7-dimethyl-2,6-octadien-1-ol
and 3-methyl-2-butenol.
[0045] Useful primary amines which contain olefinic bonds include
amines of the formula
H(CH.sub.2).sub.pCH.dbd.CH(CH.sub.2).sub.qCH.sub.2NH.sub.2- , (IV),
wherein p is 0 or an integer of 1 to 10, and q is 0 or an integer
of 1 to 30,
HR.sup.3(CR.sup.4.dbd.CR.sup.5R.sup.6).sub.tCH.sub.2NH.sub.2 (V)
wherein R.sup.3 and each R.sup.5 are each independently a covalent
bond, alkylene or alkylidene, and R.sup.4 and R.sup.6 are each
independently hydrogen or alkyl, wherein (when applicable) R.sup.3,
R.sup.4, R.sup.5 and R.sup.6 each independently contains 1 to 20
carbon atoms, and t is 1, 2 or 3. (IV) is a preferred primary
amine, and in (IV) it is preferred that p is 0 and/or q is 5 to 17,
or p is 8 and q is 7.
[0046] Since the reaction of the unsaturated alcohol or primary
amine with the first polymer is usually run at elevated
temperatures, and it is preferable that the alcohol or amine not be
volatilized before it has a chance to react with the first polymer,
it is preferred that the boiling point of this compound be high
enough so that volatilization will be relatively slow. This of
course means that the molecular weight of the amine or alcohol be
such that the boiling point is relatively high. Thus it is
preferred that the atmospheric boiling point (if necessary
extrapolated from a boiling point at lower pressure) of the
unsaturated primary amine or unsaturated alcohol be above the
process temperature, more preferably at least about 50.degree.
above, for reaction of the first polymer [step (a)]. The
olefinically unsaturated alcohol is a preferred reactant with the
first polymer.
[0047] The first polymer is reacted with an olefinically
unsaturated alcohol and/or primary amine to form a polymer in which
the olefinically unsaturated alcohol and/or primary amine becomes a
side chain on the polymer (forming the second polymer). If an
alcohol is used, a transesterification takes place, replacing the
--OR.sup.2 group with a group derived from the alcohol (the alcohol
minus the hydroxyl hydrogen atom). If a primary amine is used, an
amidation takes place, replacing the --OR.sup.2 group with a group
derived from the primary amine (the primary amine minus one of the
hydrogen atoms on the amino nitrogen atom). The total amount of
alcohol and/or amine added to the reaction with the first polymer
will depend upon the degree of transesterification and/or amidation
desired and the percentage of alcohol and/or primary amine actually
reacted with the first polymer. Typically this will range from 0.1
to 100 mole percent of the repeat units (I) present in the first
polymer used, preferably 0.1 to about 50 mole percent, more
preferably about 0.1 to about 35 mole percent, and especially
preferably about 1 to about 20 mole percent of (I). To increase the
rate of reaction, the amount of alcohol and/or amine added can
exceed 100% of (I), but this may have other consequences (see
below).
[0048] The reaction of the first polymer may be carried out at any
temperature at which the transesterification and/or amidation takes
place, a range of about 100.degree. C. to about 350.degree. C.,
preferably about 140.degree. C. to about 280.degree. C., and more
preferably about 180.degree. C. to about 260.degree. C., being
useful. The temperature should preferably not exceed a temperature
at which significant decomposition of the polymer takes place. The
temperature which is needed may be affected by the use of a
catalyst for the transesterification or amidation reaction. Any of
the catalysts conventionally useful for these reactions may be
used, provided it does not stop the subsequent crosslinking of the
polymer. For instance, known transesterification catalysts such as
alkyl titanates, zinc acetate, alkali metal alkoxides, dibutyltin
dilaurate, stannous octoate, butylstannoic acid, and (other) Ti,
Sn, Zn, Mn and Pb compounds may be used. Some compounds such alkali
metal alkoxides (see U.S. Pat. No. 5,656,692 for the use of this
type of transesterification catalyst) may slow the crosslinking
reaction. Preferred catalysts are tetralkyl titanates such as
tetrabutyl titanate, and dibutyltin dilaurate. Typical amounts of
catalyst may be used, for example 0.03 to 5 weight percent of the
first polymer, more typically 0.1 to 2 weight percent of the first
polymer. The catalyst may be dissolved in a small amount of an
inert liquid compound or a portion of the olefinically unsaturated
compound in order to mix it with the first polymer. Inert liquids
include aromatic hydrocarbons such as xylene,
1,2,3,4-tetramethylbenzene, and isodurene, and chlorinated
hydrocarbons such as o-dichlorobenzene. The use of these catalysts
often reduces the temperatures and/or times required for the
reaction to take place.
[0049] Since the transesterification reactions are equilibrium
reactions to drive them to completion it may be preferable to
remove the byproduct alcohol R.sup.2OH from the reaction. This can
be done by allowing this (usually volatile) alcohol to volatilize.
Vacuum may be applied and/or an inert gas sweep used to help remove
this byproduct. An inert gas atmosphere may also help prevent
discoloration and/or other degradation during the reaction.
[0050] The transesterification/amidation may be carried out in a
variety of ways. To ensure complete mixing of the alcohol and/or
amine and the first polymer all of these materials (and catalyst if
present) may be dissolved in a solvent and the byproduct alcohol
distilled from the solution. While this may be a good way of
ensuring uniform reaction, dissolution of polymers and their
recovery from solution is often an expensive process, so other
methods may be desirable. One method is to heat the polymer while
mixing it (at a temperature above its melting point and/or Tg, if
any) in a polymer mixing apparatus. While the polymer is being
kneaded by the mixer the alcohol and/or amine (and catalyst if
used) may be added, and the mixing continued until the desired
degree of reaction is achieved.
[0051] A more preferred method is a continuous process in which the
first polymer, alcohol and/or amine, and catalyst (if present) are
fed to, heated, mixed, and allowed to react in a single or twin
screw extruder or similar apparatus. The screw configuration is
preferably chosen to uniformly mix the various ingredients to
ensure that a uniform second polymer is produced. The screw design
should provide for one or more reaction zones designed to minimize
loss of the unreacted olefinically unsaturated compounds. The
temperature and residence time in the extruder are controlled such
that the desired degree of reaction is obtained. In the extruder,
vacuum sections or ports may be used to remove the byproduct
alcohol R.sup.2OH, and may also be used to remove unreacted
olefinically unsaturated alcohol and/or primary amine from the
product polymer at the exit end of the extruder. Typical residence
times in an extruder are about 20 sec. to about 5 min, preferably 1
to 2 min, with additional residence time up to about 20 min (if
desired) in heated pipes and/or melt pumps.
[0052] The second polymer is then cured using a conventional sulfur
or peroxide cure for unsaturated (olefinic) polymers. The first
polymer (before reaction) and/or the second polymer may contain
other ingredients normally present in thermoplastics or elastomers,
so long as they do not interfere with the
amidation/transesterification if present in the first polymer or
the curing if present in the second polymer. For example, large
amounts of oils are usually not present when peroxide cures are
employed, since they often slow down and/or interfere with the
cure. These materials may include fillers/reinforcing agents such
as carbon black, clay, talc, glass fiber and silica, pigments or
coloring agents such as calcium sulfate and TiO.sub.2,
antioxidants, antioxonants, oils, plasticizers, release agents,
etc. Peroxide cures often employ coagents such as triallyl
iscyanurate or "HVA-2" (m-phenylene-bis-maleimide),
trimethylolpropane trimethacrylate, trimethylolpropane acrylate,
and triallyl cyanurate to speed the cure and/or improve the
properties of the vulcanizate.
[0053] The crosslinked polymer produced by the process described
herein is novel. Also novel are compositions containing the second
polymer and a sulfur cure system or a peroxide cure system.
[0054] Blends of the first polymer and the second polymer may also
be made and then cured using a sulfur or peroxide curing system,
preferably a peroxide curing system. It is preferred that in such
blends the second polymer is at least about 20 weight percent of
the polymer present, based on the total amount of first and second
polymers present. Surprisingly, even with the blend containing less
of the olefinic unsaturated containing component, the polymers
still cure rapidly and give vulcanizates with good properties.
[0055] Vulcanizates of the second polymer have good properties,
but, similar to the product of all curing reactions these
properties may vary depending on the cure used and the starting
polymer composition. A good test for the stability of the
crosslinks formed is compression set at a given temperature. In
this type of a test a (usually cured) polymer part is subjected to
compression stress while being heated to a certain temperature.
After a given period of time the stress is released, and the part
cooled. The amount of the strain that the part does not recover is
the compression set, and the lower the number the more stable the
crosslinks are to rearrangement or simply being destroyed. This
test is particularly important for parts that are to be used under
compression, such as seals and gaskets.
[0056] It has been found that aside from the particular curing
system used, the proportions of reacted and unreacted alcohol or
amine in the second polymer greatly affect the compression set
thereof. When the molar percentage of reacted alcohol or amine is
relatively high the compression set is lower. Thus it is preferred
that the second polymer contain more than about 70 mole percent,
more preferably more than about 80 mole percent, especially
preferably more than about 90 mole percent of reacted olefinically
unsaturated alcohol or primary amine. A higher level of reaction
can be achieved by subjecting the molten polymer to a vacuum, for
instance a vacuum section in an extruder. The proportions of
reacted and unreacted alcohol and/or amine can be determined by NMR
spectroscopy (see below).
[0057] It has also been found that if the first polymer is dried
before being reacted with the olefinically unsaturated alcohol
and/or amine that the amount of unreacted alcohol and/or amine in
the second polymer is reduced. It is therefore preferred to dry the
first polymer before this reaction. Before drying, the polymer may
contain about 0.2 to 0.8% water. The polymer can be dried in a
vacuum oven: overnight drying at 80.degree. C., with a vacuum and
slow nitrogen purge, can reduce the water content to about 0.01%,
which can rise to about 0.05% after exposure to ambient conditions
for a day or two. The polymer can also be dried by passing it
through an extruder, without any other ingredients, while pulling a
vacuum on vent ports placed over two or more of the extruder zones.
The screw can be run at 200-250 rpm or any convenient speed, and
the temperature profile adjusted so that the polymer's exit
temperature is about 200.degree. C. Under these conditions, the
moisture content can be reduced to about 0.01-0.02%. The drying may
also be accomplished at the back (feed) end of the extruder before
introduction of the olefinically unsaturated compound and catalyst
(if used). After heating the polymer in the first few zones of the
extruder, the moisture is removed at a vent port, followed by a
melt seal designed to separate the drying process from the
transesterification or transamidation taking place in the next
zones of the extruder. The melt seal can consist of a blister ring
or reverse elements incorporated into the extruder screws.
[0058] In order to achieve low compression set it has been found
that a minimum level of reacted olefinically unsaturated alcohol
and/or primary amine should be present in the second polymer. This
is especially true when a sulfur cure system is used. Preferably
there should be 30 mmol/100 g of second polymer or more, more
preferably about 35 mmol/100 g of second polymer or more of reacted
olefinically unsaturated alcohol and/or primary amine present. A
combination of low unreacted olefinically unsaturated alcohol
and/or primary amine, and the minimum preferred amount of reacted
olefinically unsaturated alcohol and/or primary amine often leads
to the best (lowest) compression sets and/or fast cure rate.
[0059] In another preferred composition of the second polymer it is
preferred that at least about 0.5 mole percent, preferably at least
about 1.0 mole percent, and especially preferably at least about
2.0 mole percent of R.sup.2 contain olefinic unsaturation.
EXAMPLE
[0060] A Brabender Plasticorder.RTM.. (C. W. Brabender Instruments,
Inc., South Hackensack, N.J., U.S.A.) equipped with a 3-piece Prep
Mixer.RTM. and roller blades in a 350 ml cavity is pre-heated to
200.degree. C. Under a nitrogen blanket, with roller blades turning
at reduced speed, 225 g of polyethyl acrylate elastomer and 25.0 g
of .omega.-undecylenyl alcohol are added to the Brabender. The
speed of the roller blades is increased to 75 rpm and mixing is
allowed to continue until the temperature again rises to
200.degree. C., in about 10 min. With the reactants at 200.degree.
C., 2.1 ml of 25% (w/w) titanium tetra-n-butoxide in
1,2,3,4-tetramethylbenzene is added gradually, and the mixing is
allowed to continue for an additional 20 min. Then the mixer blades
are stopped, the head disassembled, and the product discharged.
Some of the ethyl groups are replaced by the unsaturated
hydrocarbyl groups of the .omega.-undecylenyl alcohol. In the
theoretical limit (if 100% of the alcohol is reacted), 6.5% of the
ethyl groups are replaced.
[0061] 100 g of the product obtained above is sulfur-cured by first
compounding on a rubber mill with 5 g of zinc oxide, 1 g of stearic
acid, 1 g of Naugard.RTM. 445 4,4'-Bis (alpha,
alpha-dimethylbenzyl) diphenylamine, 60 g of SRF N-774
semi-reinforcing furnace black, 1.5 g of sulfur, 0.5 g of
2-mercaptobenzothiazole, and 1.5 g of Thionex.RTM. tetramethyl
thiuram monosulfide, followed by press-curing the resulting
compound for 20 min at 160.degree. C.
[0062] For the compression set test, compression set pellets are
press cured for 20 min at 160.degree. C. and some of them are
additionally post-cured in an oven for 4 hrs at 160.degree. C. A
control sample is prepared on the rubber mill from polyethyl
acrylate and the same sulfur-compound-based recipe and is similarly
cured and pellets similarly cured and optionally post-cured. The
composition of the invention exhibits a greater state of cure than
the control with a higher percentage of insolubles in solvents like
acetone, and better compression set resistance.
[0063] A second 100 g aliquot of the product obtained from the
Brabender as hereinabove described, is peroxide cured by first
compounding on a rubber mill with 0.5 g of Vanfre.RTM. VAM
polyoxyethylene octadecyl ether phosphate, 0.5 g of =Armeen.RTM.
18D octadecyl amine, 1.5 g of stearic acid, 1.0 g of Naugard.RTM.
445, 65 g of SRF Black, N-774, 5.0 g of TP-759 polyether/ester
plasticizer, 2.5 g of Vulcup.RTM. R
2,2-bis(t-butylperoxy)diisopropyl benzene, and 1.0 g of HVA-2
N,N'-m-phenylene dimaleimide, followed by press curing for 15 min
at 177.degree. C.
[0064] For the compression set test, compression set pellets are
press cured for 15 min at 177.degree. C. and some of them are
additionally post-cured in an oven for 4 hrs at 177.degree. C. A
control sample is prepared on the rubber mill from polyethyl
acrylate and the same peroxide-type curing recipe as described
above and is similarly cured and pellets similarly cured and
optionally post-cured. Oscillating disk rheometer data (ASTM D2084)
shows that the product prepared in the Brabender is cured faster
than the second polyethyl acrylate control sample, which contains
no unsaturation attached to the polymer. The composition prepared
from the product made in the Brabender exhibits a greater state of
cure than the second control--it has better compression set
resistance than the control.
* * * * *