Compositions of and a method for preparing high-temperature oil resistant elastomers from hydrogenated butadiene alkenylpyridine copolymers

A random copolymer is formed by emulsion polymerization from two monomeric classes. The first monomeric class is a conjugated diene or substituted conjugated diene containing from four to about eight carbon atoms. The second monomeric class is of the general formula ##STR1## wherein R.sub.1 is an alkenyl group containing from about two to about eight carbon atoms, and R.sub.2 is hydrogen or an alkyl group containing from one to about eight carbon atoms. The second monomeric class can be replaced with up to about 20 percent by weight of the general formula CH.sub.2 .dbd.CR.sub.3 C wherein R.sub.3 is hydrogen or --CH.sub.3 l and X is --OOR.sub.4, --ONR.sub.5 R.sub.6 or --OOR.sub.7 OR.sub.4 wherein R.sub.4 is an alkyl group containing from one to about four carbon atoms, --CH.sub.2 CF.sub.3 or --CH.sub.2 CF.sub.2 CF.sub.2 H, R.sub.5 and R.sub.6 are alkyl groups independently containing from one to about four carbon atoms and R.sub.7 is an alkylene group containing from 1 to about 4 carbon atoms. The random copolymer thus obtained is hydrogenated in the presence of a transition metal catalyst and a trialkyl aluminum and further in the absence of Lewis acids such as boron trifluoride or boron trifluoride etherate. Additionally, at least one complexing agent is employed for the transition metal catalyst.

FIELD OF THE INVENTION 
The present invention relates to compositions and to the preparation of 
random copolymers of conjugated dienes and alkenyl pyridines, optionally, 
in the presence of a substituted acrylate ester, substituted acrylamide, 
fluoroalkyl acrylate esters or alkoxyalkyl acrylates or methacrylates. The 
random copolymer so obtained is then hydrogenated so at least 95 percent 
of the aliphatic olefinic double bonds are saturated. 
BACKGROUND 
Nitrile-butadiene rubber (NBR) is an oil resistant elastomer used in 
automotive applications. It has poor high temperature properties. The 
recommended continuous use temperature is between 100.degree.-125.degree. 
C. Commercially available hydrogenated NBR (HNBR) addresses the need for a 
higher use temperature, oil resistant elastomer having a continuous use 
temperature up to about 150.degree. C. 
Removal of the backbone unsaturation in NBR by hydrogenation increases the 
heat resistance of the polymer while maintaining its low temperature and 
oil resistance properties. HNBR is mainly a random copolymer of ethylene 
and acrylonitrile. HNBR compositions that contain up to 40 weight percent 
bound acrylonitrile and 60 weight percent hydrocarbon segments have high 
oil resistance and good low temperature properties. Higher acrylonitrile 
content in the copolymer would further increase oil resistance, but would 
be detrimental to low temperature properties. 
U.S. Pat. No. 3,416,899 (Schiff, Dec. 17, 1968) relates to improved gel 
compositions useful as incendiary fuels, as solid fuels for heating, as a 
fracturing liquid for subterranean formations, and the like. In another 
aspect, this reference relates to the preparation of hydrocarbon gel 
compositions by hydrogenating a hydrocarbon solution of an unsaturated 
rubbery polymer in the presence of a catalyst comprising a reducing metal 
compound and a salt of a Group VIII metal. 
U.S. Pat. No. 3,766,300 (De La Mare, Oct. 16, 1973) discloses a process for 
the hydrogenation of copolymers prepared from conjugated dienes and 
certain copolymerizable polar monomers such as vinyl pyridines, 
acrylonitriles, and alpha-olefin oxides which comprises an initial step of 
forming a complex between at least one Lewis acid and the polar portions 
of the copolymer and thereafter subjecting the complex to hydrogenation. 
More particularly, this reference is especially concerned with a process 
for the hydrogenation of block copolymers derived from these monomers. 
Japanese Patent No. 13,615 (Aug. 2, 1967; filed Feb. 15, 1963) relates to 
copolymers of butadiene and vinyl pyridine that were reduced to give 
waterproof, stable reduced copolymers. These products were useful for 
coating pills. The reduced copolymers were obtained by the catalytic 
hydrogenation in the presence of Raney nickel catalyst. 
A paper titled "Oil-Resistant Rubbers from 2-Methyl Vinyl Pyridine," James 
E. Pritchard and Milton H. Opheim, Industrial and Engineering Chemistry, 
Volume 46, No. 10, pages 2242-2245, relates to quaternization of liquid 
polymers. Copolymers of butadiene and 2-methyl-5-vinyl pyridine (MVP) 
react with quaternizing agents to form polymeric salts of the type: 
##STR2## 
where R is an aliphatic or aromatic radical and X represents halide, alkyl 
sulfate, or aryl sulfonate groups. 
SUMMARY OF THE INVENTION 
Random copolymer compositions which function as oil-resistant elastomers 
are prepared by the emulsion polymerization of two monomeric classes. The 
first monomeric class consists of a conjugated diene or branched 
conjugated diene or mixtures thereof containing from 4 to 8 carbon atoms. 
The second monomeric class is characterized by the formula 
##STR3## 
wherein R.sub.1 is an alkenyl group containing from about 2 to about 8 
carbon atoms, and R.sub.2 is hydrogen or an alkyl group containing from 1 
to about 8 carbon atoms. The second monomeric class can be replaced with 
up to about 20 percent by weight of CH.sub.2 .dbd.CR.sub.3 CX wherein 
R.sub.3 is hydrogen or methyl and X is --OOR.sub.4, --ONR.sub.5 R.sub.6 or 
OOR.sub.7 OR.sub.4 wherein R.sub.4 is an alkyl group containing from 1 to 
about 4 carbon atoms, --CH.sub.2 CF.sub.3 or --CH.sub.2 CF.sub.2 CF.sub.2 
H, R.sub.5 and R.sub.6 are alkyl groups independently containing from 1 to 
about 4 carbon atoms and R.sub.7 is an alkylene group containing from 1 to 
about 4 carbon atoms. The random copolymer so formed is then hydrogenated 
using a transition metal catalyst and at least one complexing agent.

DETAILED DESCRIPTION OF THE INVENTION 
This invention deals with compositions and a method for preparing high 
temperature, oil-resistant elastomers by the copolymerization of two 
monomeric classes followed by the hydrogenation of the copolymer. Direct 
polymerization of ethylene with acrylonitrile to give HNBR is not feasible 
due to the difference in reactivities of the monomers under the 
copolymerization conditions. This is generally true in the case of 
copolymerization of ethylene with any polar alpha, beta unsaturated 
monomer. Direct copolymerization of ethylene and polar alpha, beta 
unsaturated monomers (including acrylonitrile) using transition metal 
catalysts have been unsuccessful. 
Free radical polymerization at very high pressures, ca 2000 atmospheres, 
results in comparable reactivity for ethylene and acrylonitrile, but the 
polymerization process is plagued with side reactions that preclude high 
molecular weight polymer formation. The polymer obtained thus is a poor 
candidate for cross-linking to an elastomer. 
Free radical polymerization can be performed at lower pressure, ca 60 
atmospheres, in a solvent using a Lewis acid as the complexing agent for 
the polar monomer, acrylonitrile. As an almost perfectly alternating 
copolymer is formed, the low temperature properties are poorer than the 
corresponding random copolymer. Also, tensile strength is reduced in the 
perfectly alternating copolymer, due to the lack of polyethylene segments 
which is responsible for the high strength of the random copolymer. 
Conjugated dienes readily copolymerize with polar alpha, beta monomers in 
emulsion to give high molecular weight copolymers. Subsequent 
hydrogenation of the backbone unsaturation in these polymers is an 
alternate route to copolymers of ethylene with polar alpha, beta 
unsaturated monomers. 
The first monomeric class is a straight chain conjugated diene, a branched 
chain conjugated diene, or mixtures thereof. This diene contains from 4 to 
8 carbon atoms. Examples of straight chain dienes are 1,3-butadiene, 
1,3-pentadiene, 1,3-hexadiene, 1,4-hexadiene, 1,3-heptadiene, 
2,4-heptadiene, 1,3-octadiene, 2,4-octadiene, and 3,5-octadiene. Some 
representative examples of branched chain dienes are isoprene, 
2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-hexadiene, 
3-methyl-1,3-hexadiene, 2-methyl-2,4-hexadiene, 3-methyl-2,4-hexadiene, 
2,3-dimethyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 
2-ethyl-1,3-pentadiene, and 3-ethyl-1,3-pentadiene. The preferred dienes 
for the practice of this invention are butadiene and isoprene. 
The second monomeric class is of the general formula 
##STR4## 
where R.sub.1 is an alkenyl group containing from about 2 to about 8 
carbon atoms, preferably from about 2 to 6, and most preferably from 2 to 
about 4 carbon atoms. Particularly, R.sub.1 is vinyl. R.sub.2 is hydrogen 
or an alkyl group containing from 1 to about 8 carbon atoms. When R.sub.2 
is an alkyl group, it preferably contains from 1 to about 6 carbon atoms 
and most preferably from 1 to about 4 carbon atoms. When R.sub.2 is alkyl, 
a particular group is methyl. 
The general formula (I) of the second monomeric class can be replaced with 
up to about 20 percent by weight of general formula (II) CH.sub.2 
.dbd.CR.sub.3 CX. R.sub.3 is hydrogen or methyl and X is --OOR.sub.4, 
--ONR.sub.5 R.sub.6 or --OOR.sub.7 OR.sub.4 wherein R.sub.4 is an alkyl 
group containing from 1 to about 4 carbon atoms, --CH.sub.2 CF.sub.3 or 
--CH.sub.2 CF.sub.2 CF.sub.2 H, R.sub.5 and R.sub.6 are alkyl groups 
independently containing from 1 to about 4 carbon atoms and --OOR.sub.7 
OR.sub.4 is an alkylene group containing from 1 to about 4 carbon atoms. 
When R.sub.3 is hydrogen or methyl and X is --OOR.sub.4, some examples of 
general formula II are acrylates, methacrylates, fluorinated acrylates or 
fluorinated methacrylates. When R.sub.3 is hydrogen or methyl and X is 
--ONR.sub.5 R.sub.6, general formula II may be tertiary acrylamides or 
tertiary methacrylamides. When X is --OOR.sub.7 OR.sub.4, preferably 
R.sub.7 is an alkylene group containing from 1 to about 2 carbon atoms and 
R.sub.4 is an alkyl group containing from 1 to about 2 carbon atoms. 
Preferably at least 3 percent of general formula (II) is present in the 
second monomeric class and most preferably at least 7 percent of general 
formula (II) is present in the second monomeric class. 
The hydrogenated random copolymers of this invention have utility as high 
temperature oil-resistant elastomers. The hydrogenated random copolymers 
of this invention may be solids or liquids, depending on molecular weight. 
These hydrogenated random copolymers serve as thermooxidatively stable oil 
resistant elastomers or as impact modifiers for plastics. Products made 
from these elastomers find use for seals, gaskets, and hoses. The liquid 
polymers can be used as processing aids and/or modifiers in rubber and 
plastic compounding. 
Conjugated 1,3-dienes copolymerize readily with alpha,beta unsaturated 
monomers other than acrylonitrile. Examples of two such monomer classes 
are vinyl pyridine or acrylates. These copolymers, like NBR, are also oil 
resistant. In addition, hydrogenation of the polymer backbone of the 
conjugated diene/vinyl pyridine and conjugated diene/acrylate copolymer is 
possible with inexpensive homogeneous catalysts based on iron, cobalt or 
nickel. Hence, high temperature oil resistant elastomers can be obtained 
at a cost lower than that of HNBR. 
The first step in the preparation of an oil-resistant elastomer is in 
forming a random copolymer of the two monomeric classes. The random 
copolymer is formed by emulsion polymerization. The weight ratio of the 
first monomeric class:the second monomeric class is from about 
25-85:75-15, preferably 40-60:60-40, and most preferably 55-60:45-40. 
The random copolymer is made in a conventional manner. That is, the 
above-noted monomers are added to suitable amounts of water in a 
polymerization vessel along with one or more conventional ingredients and 
polymerized. The amount of polymerized solids or particles is generally 
from about 15 percent to about 50 percent with from about 25 to about 35 
percent by weight being desired. The temperature of polymerization is 
generally from about 5.degree. C. to about 80.degree. C. with from about 
5.degree. C. to about 20.degree. C. being preferred. Typically in excess 
of 60 percent and usually from about 70 percent to about 95 percent 
conversion is obtained with from about 80 percent to about 85 percent 
conversion being preferred. The polymerization is generally initiated by 
free radical catalysts which are utilized in conventional amounts. 
Examples of such catalysts include organic peroxides and hydroperoxides 
such as benzoyl peroxide, dicumyl peroxide, cumene hydroperoxide, 
paramenthane hydroperoxide, and the like, used alone or with redox 
systems; diazo compounds such as azobisisobutyronitrile, and the like; 
persulfate salts such as sodium, potassium, and ammonium persulfate, used 
alone or with redox systems; and the use of ultraviolet light with 
photo-sensitive agents such as benzophenone, triphenylphosphine, organic 
diazos, and the like. 
Inasmuch as the random copolymers are prepared via an emulsion latex 
polymerization route, anionic emulsifying aids are utilized. Thus, various 
conventional anionic surfactants known to the art as well as to the 
literature are utilized. Generally, any suitable anionic surfactant can be 
utilized such as those set forth in McCutcheons, "Detergents and 
Emulsifiers," 1978, North American Edition, Published by McCutcheon's 
Division, MC Publishing Corp., Glen Rock, N.J., U.S.A., as well as the 
various subsequent editions thereof, all of which are hereby fully 
incorporated by reference. Desirably, various conventional soaps or 
detergents are utilized such as a sodium alkyl sulfate, wherein the alkyl 
has from 8 to 22 carbon atoms such as sodium lauryl sulfate, sodium 
stearyl sulfate, and the like, as well as various sodium alkyl benzene 
sulfonates, wherein the alkyl has from 8 to 22 carbon atoms such as sodium 
dodecyl benzene sulfonate, and the like. Other anionic surfactants include 
sulfosuccinates and disulfonated alkyl benzene derivatives having a total 
of from 8 to 22 carbon atoms. Various phenyl type phosphates can also be 
utilized. Yet other anionic surfactants include various fatty acid salts 
having from 12 to 22 carbon atoms as well as various rosin acid salts 
wherein the salt portion is generally lithium, sodium, potassium, 
ammonium, magnesium, and the like. The selection of the anionic surfactant 
generally depends on the pH of the polymerization reaction. Hence, fatty 
acid salts and rosin acid salts are not utilized at low pH values. 
The amount of the surfactant can vary depending upon the size of random 
copolymer particles desired, but typically is from about 1 percent to 
about 6 percent and desirably from about 2 percent to about 3 percent by 
weight for every 100 parts by weight of the random copolymer forming 
monomers. 
Other anionic emulsifying aids are various anionic electrolytes which 
control particle size by controlling the solubility of the soap. Examples 
of various conventional electrolytes generally include sodium, potassium, 
or ammonium naphthalene sulfonates. Other suitable electrolytes include 
sodium sulfate, sodium carbonate, sodium chloride, potassium carbonate, 
sodium phosphate, and the like. The amount of electrolyte is generally 
from about 0.1 to about 1.0 parts by weight and preferably from about 0.2 
to about 0.5 parts by weight for every 100 parts by weight of the random 
copolymer forming monomers. 
Molecular weight modifiers are also utilized to maintain the molecular 
weight within desirable limits as otherwise the viscosity of the polymer 
would be exceedingly high for subsequent handling, processing, and the 
like. Generally, known conventional molecular weight modifiers can be 
utilized such as various mercaptans which have from about 8 to about 22 
carbon atoms, generally in the form of an alkyl group. Various sulfide 
compounds can also be utilized such as diisopropylxanthogendisulfide and 
di-sec-butylxanthogendisulfide. The amount of the molecular modifiers is 
generally an effective amount such that the Mooney viscosity, that is 
ML.sub.4 @ 100.degree. C. is from about 10 to about 120 and desirably from 
about 20 to about 80. 
Yet another conventional emulsion latex additive is various short stop 
agents which are added generally to stop the polymerization and to tie up 
and react with residual catalysts. The amount of the short stop agents is 
from about 0.05 to about 1.0 parts by weight per 100 parts by weight of 
said random copolymer forming monomers. Examples of specific short stop 
agents include hydroxyl ammonium sulfate, hydroquinone and derivatives 
thereof, e.g., ditertiaryamylhydroquinone, various carbamate salts such as 
sodium diethyldithiocarbamate, various hydroxyl amine salts, and the like. 
Various antioxidants can be added and such are known to the art as well as 
to the literature including various phenolic type antioxidants such as 
di-tert-butyl-paracresol, various diphenylamine antioxidants such as 
octylated diphenylamine, various phosphite antioxidants such as trisnonyl 
phenyl phosphite, and the like. Once the short stop has been added to the 
latex solution, excess monomer is stripped from the resultant latex, as 
for example by steam. 
According to the concepts of the present invention, a cationic coagulant 
polymer is utilized to coagulate the anionic emulsifying aids such as the 
various anionic surfactants and the various anionic electrolytes utilized. 
Polymeric cationic type coagulants are utilized according to the present 
invention inasmuch as they have a positive site which generally reacts 
with the negative or anionic site of the surfactant, electrolyte, etc., 
and thereby neutralize the same and render it innocuous. That is, 
according to the concepts of the present invention, the anionic 
emulsifying aids are not physically removed but rather are chemically 
reacted with a cationic polymeric coagulant to form an adduct which is 
generally dispersed throughout the random copolymer particle. 
An important aspect of the present invention is that large 
stoichiometrically equivalent amounts of cationic polymeric coagulants are 
utilized. That is, large weight equivalents are required in order to yield 
a random copolymer having improved properties. Generally, from about 0.75 
to about 1.5 weight equivalents, desirably from about 0.85 to about 1.25, 
and preferably from about 0.95 to about 1.05 weight equivalents of the 
cationic polymeric coagulant is utilized for every weight equivalent of 
said anionic emulsifying aids. Equivalent weight amounts less than those 
set forth herein do not result in effective neutralization, tying up, or 
negate the effect which the various anionic emulsifying aids have upon the 
properties of the dried rubber particles. 
The cationic polymeric coagulants utilized in the present invention 
generally contain a tetravalent nitrogen and are sometimes referred to as 
polyquats. Cationicity of the quaternary nitrogen is generally independent 
of pH, although other parts of the polymer molecule may exhibit 
sensitivity to pH such as hydrolysis of ester linkages. Typically, 
cationic polymers are prepared either by quaternization of poly(alkylene 
polyamines), poly(hydroxyalkylene polyamines), or poly(carbonylalkylene 
polyamine) with alkyl halides or sulfates, or by step-growth 
polymerization from dialkylamines, tetraalkyl amines, or derivatives 
thereof, with suitable bifunctional alkylating agents, and with or without 
small amounts of polyfunctional primary amines (such as ammonia, ethylene 
diamines, and others) for molecular weight enhancement. Polyamines 
produced from ammonia and ethylene dichloride, quaternized with methyl 
chloride, and polyquaternaries produced directly from dimethylamine and 
1-chloro-2,3-epoxypropane are generally of commercial significance. 
Epichlorohydrin reacts with ammonia and primary, secondary, or 
polyfunctional amines to form polyamines or polyquats. The polyamines can 
be subsequently quaternized to yield a cationic polymeric coagulant of the 
present invention. As known to those skilled in the art and to the 
literature, literally hundreds of cationic polymeric coagulants exist and 
generally the same can be utilized in the present invention. Examples of 
specific polymeric cationic coagulants include 
poly(2-hydroxypropyl-1-N-methylammonium chloride), 
poly(2-hydroxypropyl-1,N,N-dimethylammonium chloride), 
poly(diallyldimethylammonium chloride), poly(N,N-dimethylaminoethyl 
methacrylate) quaternized, and a quaternized polymer of epichlorohydrin 
and a dialkylamine wherein the alkyl group has from 1 to 5 carbon atoms 
with methyl being preferred. The method of preparing cationic polymeric 
coagulants, general types of such compounds as well as specific individual 
compounds are set forth in the following documents which are hereby fully 
incorporated by reference with regard to all aspects thereof: 
Encyclopedia of Polymer Science and Technology, John Wiley & Sons, New 
York, 1987, Volume 11, 2nd Edition, pages 489-503. 
Encyclopedia of Polymer Science and Technology, John Wiley & Sons, New 
York, 1987, Volume 7, 2nd Edition, pages 211-229. 
Kirk Othermer's Encyclopedia of Chemical Technology, 3rd Edition, Volume 
10, John Wiley & Sons, New York, 1980, pages 489-523. 
A text entitled Commercial Organic Flocculants, Josef Vostrcil and 
Frantisek Juracka, Noyes Data Corporation, Park Ridge, N.J., 1976, in its 
entirety. 
The cationic polymeric coagulants utilized in the present invention 
generally have a molecular weight of from about 1,000 to about 10,000,000. 
According to the present invention, the cationic polymeric coagulant 
treated random copolymer latex generally results in a slurry of rubber 
crumbs in a clear aqueous liquid. The crumbs contain the various anionic 
emulsifying aids physically incorporated therein. Such crumbs can be 
separated in any conventional manner as by filtering. Inasmuch as the 
anionic emulsifying aids have been rendered innocuous, multiple washing 
steps or other expensive, tedious process steps such as solvent extraction 
are not utilized. 
The random copolymer of the present invention once dried as by conventional 
means, have improved properties such as good water resistance, good 
adhesion properties, non-interference with cure systems when cured, reduce 
fouling of molds during the manufacture of parts, improved electrical 
insulating properties, and the like. Such polymers can accordingly be 
utilized as adhesives, that is polymeric adhesives, binders, films, e.g., 
electrical insulating films, coatings such as for electrical circuit 
boards along with other conventional coating additives and fillers known 
to the art and to the literature, and the like. Suitable adhesive uses 
include metal-to-metal adhesion, metal-to-fabric adhesion, 
metal-to-plastic adhesion, and the like. Additionally, the polymers of 
this invention have utility in the automotive area such as in hoses, 
gaskets, seals, and timing belts. 
The random copolymer can be prepared with a mercaptan chain transfer agent 
composition comprising (a) at least one mercaptan chain transfer agent and 
(b) at least one non-polymerizable material which is miscible with the 
mercaptan chain transfer agent. Suitable mercaptans include water soluble 
mercaptans such as 2-mercaptoethanol, 3-mercaptopropanol, 
thiopropyleneglycol, thioglycerine, thioglycolic acid, thiohydracrylic 
acid, thiolactic acid, and thiomalic acid, and the like. Suitable 
non-water soluble mercaptans include isooctyl thioglycolate, n-butyl 
3-mercaptopropionate, n-butyl thioglycolate, glycol dimercaptoacetate, 
trimethylolpropane trithioglycolate, alkyl mercaptans, and the like. The 
preferred mercaptans are 2-mercaptoethanol and t-dodecylmercaptan, 
however, any chain transfer agent having a mercapto (--SH) group would be 
acceptable. 
The chain transfer composition, in addition to the mercaptan, may contain 
at least one non-polymerizable material which is miscible with the 
mercaptan and is substantially insoluble in water. The term 
non-polymerizable as used herein means that the material does not form a 
part of the random copolymer chain in the sense that a traditional 
comonomer would form. The non-polymerizable material may, in some cases, 
graft polymerize onto the random copolymer chain but this is not normally 
considered a copolymer. The term substantially insoluble in water as used 
in this specification means that the material has less than 5 percent 
solubility in water. The non-polymerizable material may be a monomer, 
oligomer or a polymer. Suitable non-polymerizable materials include 
dioctyl phthalate, low molecular weight poly(caprolactone), polysilicones, 
esters of glycerols, polyesters, water insoluble esters of fatty acids 
with --OH terminated polyoxyethylene and polyoxypropylene, esters of 
polyols, esters of monoacids and polyacids, esters of organic 
polyphosphates, phenyl ethers, ethoxylated alkylphenols, sorbitan 
monostearate and sorbitan monooleate and other sorbitol esters of fatty 
acids. The choice of material is not critical as long as the material is 
non-polymerizable with the monomers and is substantially insoluble in 
water. 
The chain transfer composition must contain at least enough 
non-polymerizable material to encapsulate the mercaptan chain transfer 
agent. This amount varies according to the type and amount of chain 
transfer agent used. Usually, the chain transfer composition must contain 
at least an equal amount in weight of non-polymerizable material as chain 
transfer agent in order to encapsulate or host the chain transfer agent. 
Preferably, the composition contains at least twice as much weight of 
non-polymerizable material as chain transfer agent. Other non-essential 
ingredients may be used in the chain transfer compositions of this 
invention but are not preferred. 
The chain transfer compositions are formed by mixing the two essential 
ingredients together. The method used to mix the ingredients is not 
critical and may be any of the known methods used by those skilled in the 
art. The ingredients may even be charged to the polymerization reactor and 
mixed before adding the other polymerization ingredients but is preferably 
mixed outside the reactor. 
Because of the detrimental effects that mercaptans, such as 
2-mercaptoethanol have on colloidal stability, it is necessary to mix the 
2-mercaptoethanol with the non-polymerizable material before adding it to 
the reaction medium. The non-polymerizable material serves as a host 
material for the chain transfer agent. This procedure surprisingly 
eliminates the adverse effects of 2-mercaptoethanol on colloidal 
stability. It is believed that the non-polymerizable material averts the 
adverse effect of 2-mercaptoethanol on colloidal stability via 
encapsulation, complexation or interaction and, thus, allows relatively 
high levels of 2-mercaptoethanol to be introduced to the reaction medium 
prior to the start of polymerization. The term "encapsulation" as used 
herein is not intended as the traditional meaning of encapsulation which 
is to coat or contain and the result is a heterogeneous system. The chain 
transfer composition of this invention is homogeneous. 
The level of chain transfer composition used to make the random copolymer 
will be described in terms of the level of mercaptan in the composition. 
The level of mercaptan used is greater than 0.03 part by weight per 100 
parts by weight of diene monomer. The preferred levels of mercaptan range 
from about 0.03 to about 5.00 parts by weight per 100 parts of monomer, 
and, preferably, from 0.10 to 1.50 parts. 
When high amounts of mercaptan, such as 2-mercaptoethanol, are used, it is 
desirable to not charge the entire amount of chain transfer agent at the 
beginning of polymerization since 2-mercaptoethanol has a diminishing 
effect on molecular weight above about the 1.5 parts level. Therefore, if, 
for example, 3.0 parts were used, it would be advisable to add only up to 
1.5 parts at the beginning of polymerization and to gradually add the 
remainder during polymerization. Amounts added at the beginning which are 
greater than 1.5 parts do not result in colloidal instability. However, 
for the most efficient use of chain transfer agent, it is preferred to not 
add more than 1.5 parts before the beginning of polymerization. This 
preferred initial level could, of course, be different for different 
mercaptans. The above described preferred procedure is for 
2-mercaptoethanol. 
If less than 0.25 part by weight of chain transfer agent is used, then all 
of the chain transfer agent will be added in the form of the chain 
transfer composition before the beginning of polymerization. If more than 
0.25 part is used, then at least 0.25 part will be added in the form of 
the chain transfer composition before the beginning of polymerization and 
the remainder may be added later. To gain the most efficiency of the chain 
transfer agent, no more than 1.5 parts by weight should be added before 
the start of polymerization. For best results, at least 50 percent of the 
chain transfer agent, preferably 100 percent, is added to the 
polymerization medium prior to the start of polymerization. Any amount not 
added at the start and not encapsulated should be added after the 
polymerization has reached about 10 percent conversion to maintain 
collodial stability. Except for the use of the chain transfer composition, 
the polymerization is much the same as in any conventional polymerization 
of a diene monomer in an aqueous medium. 
Another class of chain-transfer agents that are used in the process of this 
invention are mercapto organic compounds having at least one ether linkage 
that have the structural formula 
EQU X--(CH.sub.2).sub.m --(OY).sub.n --SH 
wherein X represents hydrogen or --SH, Y represents an alkylene group 
having 1 to 6 carbon atoms, and m and n each represents a number in the 
range of 1 to 10. 
A preferred group of ether linkage chain-transfer agents includes mercapto 
organic compounds that have the structural formula 
EQU X--(CH.sub.2).sub.m '--(OY').sub.n '--SH 
wherein X represents hydrogen or --SH, Y' represents an alkylene group 
having 2 to 4 carbon atoms, and m' and n' each represents a number in the 
range of 2 to 4. 
Illustrative of the ether linkage chain-transfer agents that can be used in 
the practice of this invention are the following compounds: 
mercaptomethyl ethyl ether, 
2-mercaptoethyl ethyl ether, 
2-mercaptoethyl propyl ether, 
2-mercaptoethyl butyl ether, 
3-mercaptopropyl methyl ether, 
3-mercaptopropyl ethyl ether, 
3-mercaptopropyl butyl ether, 
2-mercaptopropyl isopropyl ether, 
4-mercaptobutyl ethyl ether, 
bis-(2-mercaptoethyl) ether, 
bis-(3-mercaptopropyl) ether, 
bis-(4-mercaptobutyl) ether, 
(2-mercaptoethyl) (3-mercaptopropyl) ether, 
(2-mercaptoethyl) (4-mercaptobutyl) ether, 
ethoxypolypropylene glycol mercaptan, 
methoxypolyethylene glycol mercaptan, and the like and mixtures thereof. 
Among the preferred ether linkage chain-transfer agents are 2-mercaptoethyl 
ethyl ether and bis-(2-mercaptoethyl) ether. 
The amount of the ether linkage chain-transfer agent that is used in the 
polymerization reaction is that which will provide a polymer having the 
desired molecular weight or degree of polymerization. In most cases from 
0.01 percent to 2 percent by weight, based on the weight of the monomer 
component, is used. When a low molecular weight product that has a 
relative viscosity in the range of 1.20 to 1.60 is desired, the amount of 
chain transfer agent used is preferably in the range of 0.25 percent to 
1.75 percent by weight, based on the weight of the monomer. Amounts in the 
range of 0.05 percent to 0.15 by weight, based on the weight of the 
monomer, are preferably used to produce polymers having high molecular 
weights. 
The invention will be better understood by reference to the following 
examples. 
The below Table I shows the preparation of a random copolymer of butadiene 
and 2-vinylpyridine. Items 1 through 9 are initially charged into a 15 
gallon reactor under nitrogen and cooled to 5.degree. C. Polymerization is 
initiated by adding items 10 through 12. These three items promote 
peroxide breakdown thereby generating initiator radicals. The conversion 
is monitored by measuring total solids content every hour. At 35 percent 
conversion, the additional items 1 through 5 are added. After 20 hours, at 
5.degree. C., 80 percent conversion is obtained and the reaction is 
terminated by adding item 13. After removal of volatiles, the latex is 
coagulated in hot water (70.degree. C.) containing 1.5 weight percent of 
aluminum sulfate to form a crumb. The crumb is filtered, washed with water 
and dried in air at 100.degree. C. for 4 hours. 
TABLE I 
__________________________________________________________________________ 
EXAMPLE 1 
Parts by Weight 
Added 
Added at 
Item 
Material Purity % 
Initially 
35% Conv. 
Total 
__________________________________________________________________________ 
1 Soft Water 100 186.48 
12.83 199.31 
2 Sipex SB Emulsifier 
30 2.0 1.0 3.0 
3 Sodium Naphthalene 
100 .67 .33 1.0 
Sulfonate Secondary 
Emulsifier 
4 Sodium Carbonate 
100 .16 .08 .24 
Electrolyte 
5 Sulfole 120 Chain 
100 .18 .12 .30 
Transfer Agent 
6 Cumene Hydroperoxide 
82.5 .115 -- .115 
Initiator 
7 Sodium Hydrosulfite 
100 .007 -- .007 
Oxygen Scavenger 
8 Butadiene Monomer 
100 55 -- 55 
9 2-Vinylpyridine Monomer 
100 45 -- 45 
10 Trisodium Ethylenediamine 
100 .01 -- .01 
Tetraacetate Trihydrate 
Complexing Agent for iron 
salts 
11 Sodium Ferric Ethylene 
100 .015 -- .015 
Diamine Tetraacetate 
12 Sodium Formaldehyde 
100 .105 -- .105 
Sulfoxylate Reducing 
Agent for Ferric Salts 
13 Hydroxyl Ammonium 
100 -- -- .3 
Sulfate Short Stop 
__________________________________________________________________________ 
Examples 2 through 5 essentially follow the procedure of Example 1 except 
for the monomers and level of monomers employed. Table II outlines 
Examples 2 through 5. 
TABLE II 
______________________________________ 
Ratio of First 
Example 
First Second & 
No. Monomer Monomer Second Monomer 
______________________________________ 
2 Butadiene 2-vinylpyridine 
40:60 
3 Isoprene 2-vinylpyridine 
50:50 
4 Isoprene 4-vinylpyridine 
55:45 
5 2,3-dimethyl 
2-methyl-5-vinyl- 
50:50 
1,3-butadiene 
pyridine + 3% 
methylmethacrylate 
______________________________________ 
The random copolymer obtained has a high cis-trans-1,4 microstructure 
rather than 1,2 and/or 3,4 microstructure (depending upon the diene). The 
combined mole percent of cis-trans 1,4-microstructure to vinyl 
microstructure has been determined to be 3.7:1 by proton magnetic 
resonance when the copolymers have a weight ratio of 60 percent butadiene 
to 40 percent 2-vinyl-pyridine by weight. The cis and trans microstructure 
get hydrogenated to linear polyethylene segments which are responsible for 
the improved mechanical properties of the elastomer due to stretch 
crystallinity (A. H. Weinstein, Rubber Chemical Technology 57, 203 
(1984)). 
The random copolymer once obtained is then subjected to hydrogenation in 
the presence of a transition metal catalyst and trialkylaluminum catalyst 
in the presence of at least one complexing agent and further in the 
absence of BF3 or BF3 etherate. 
Either a homogeneous or a heterogeneous catalyst may be used for the 
hydrogenation although a homogeneous catalyst is preferred. Since a 
homogeneous catalyst dissolves in solution, good contact is obtained with 
the random copolymer. The homogeneous catalysts are transition metal 
catalysts of either iron, cobalt, or nickel. These metals are present as 
halides, acetates, or acetylacetonates. Other homogeneous catalysts that 
can be employed are palladium, platinum or rhodium present as 
tetrakistriphenylphosphine palladium (0), tetrakistriphenylphosphine 
platinum (0) or tristriphenylphosphinerhodium chloride. 
Conventional homogeneous catalysts based on, for example, reduced cobalt 
salts are inexpensive compared to rhodium or palladium, but are only 
suitable for the hydrogenation of hydrocarbon polymers, e.g., a nickel 
catalyst is commercially used in the hydrogenation of Krayton, a triblock 
butadiene-styrene-butadiene copolymer. Hydrogenation of the polymer 
backbone of NBR is not possible using these catalysts, as the nitrile 
group in NBR acts as a catalyst poison, and, in some cases is itself 
reduced. 
HNBR is commecially synthesized by the hydrogenation of NBR in solution. 
The relatively high cost of HNBR compared to NBR is partly due to the 
solution hydrogenation process, the major contribution to cost being the 
catalyst (rhodium or palladium). 
The transition metal catalyst is employed with trialkyl aluminum, wherein 
the alkyl group contains from 1 to about 4 carbon atoms, which functions 
as a reducing agent. Other reducing agents that can be employed are 
dialkyl aluminum hydride, the dialkyl aluminum alkoxides of 1 to 4 carbon 
atoms, sodium borohydride, and lithium aluminum hydride. Additionally, 
other reductants are alkyl lithium, dialkyl magnesium, and alkyl magnesium 
halide wherein the alkyl groups are from 1 to 4 carbon atoms, and the 
halide is chloride or bromide. 
The mole ratio of transition metal catalyst: reducing agent is usually from 
1:10, preferably 1:6, and most preferably from 1:4. 
The transition metal catalyst complexes with at least one complexing agent. 
Without the complexing agent, addition of the catalyst to the polymer 
solution causes gelation. This is due to the metal ion of the transition 
metal catalyst complexing with the polar groups on the polymeric chains. A 
gelled polymer is difficult to hydrogenate to a high degree. Also, a 
partially crosslinked polymer results. These factors cause the elastomer 
to be poorer in heat aging and physical properties when compared to the 
polymers of this invention. 
In the present invention the complexing agents complex with the catalyst in 
order to prevent the catalyst from bonding to the pyridine ring. Thus the 
amount of complexing agent employed is related to the relatively low 
catalyst level. Generally, the mole ratio of catalyst:complexing agent is 
from 1:10, preferably 1:8; and most preferably 1:6. 
The complexing agents for the catalysts are hexamethylphosphoric triamide, 
tetramethylethylenediamine, phosphines of the general formula 
(R.sub.7).sub.3 P, phosphites of the general formula (R.sub.7 O).sub.3 P 
wherein R.sub.7 is an alkyl group containing from 1 to about 6 carbon 
atoms, a phenyl group or a substituted aromatic group wherein the 
substituent is an alkyl group containing from 1 to about 2 carbon atoms 
such as o-tolyl. 
Solvents for the hydrogenation are well known in the art. An exemplary list 
of solvents are xylenes, toluenes, anisole, dioxane, tetrahydrofuran, 
hydrocarbons such as hexanes, heptanes, and octanes and chlorinated 
hydrocarbons such as chlorobenzene and tetrachloroethane, trisubstituted 
amines such as triethylamine and tetramethylethylene diamine. The 
temperature of hydrogenation is generally from about 25.degree. C. to 
about 150.degree. C. with from about 25.degree. C. to about 50.degree. C. 
being preferred. 
Removal of the transition metal catalyst is difficult and expensive. This 
is due to the high molecular weight of the polymer and also that the 
catalyst is intimately associated with the polymer. A catalyst, when left 
in contact with the hydrogenated polymer, shows a degradative action. This 
action is discussed in a paper by Zenairo Osawa titled "Rule of Metals and 
Metal Deactivators in Polymer Degradation." An approach of this invention 
was the partial removal of the catalyst within the polymer, and also to 
render the residual catalyst innocuous, that is, to deactivate the 
catalyst by the addition of a second complexing agent after hydrogenation 
in the absence of air. If the catalyst is not rendered innocuous, the 
polymer shows poor heat aging and high oil swell. Some examples of the 
second complexing agents are weak organic acids containing from 1 to about 
4 carbon atoms such as formic acid, acetic acid, and propionic acid; 
diacids containing from 2 to about 6 carbon atoms such as oxalic acid, 
malonic acid, succinic acid, glutaric acid, and adipic acid and also 
sodium or potassium salts of the above mono- or diacids; trisodium 
ethylene-diaminetetraacetate; amino acids of 1 to about 4 carbon atoms 
such as glycine, alanine, alpha-glutaric acid, beta-glutaric acid, and 
gamma-glutaric acid; citric acid; pyridine or substituted pyridine wherein 
the substituent contains 1 to 2 carbon atoms; pyridine carboxylic acids 
such as nicotinic acid and the corresponding sodium or potassium salts; 
alkyl or aromatic nitriles containing from 1 to 6 carbon atoms; 
substituted ureas or thioureas such as N,N-dialkyldithiocarbamate metal 
salts of 1 to 4 carbon atoms wherein the metal is lithium, sodium, or 
potassium; sodium or potassium salt of dimethylglyoxime; 
hexamethylphosphoric triamide; tetramethylethylenediamine; phosphines 
P(R.sub.8).sub.3 and phosphites P(OR.sub.8).sub.3 wherein R.sub.8 is 
aliphatic of 1 to 4 carbon atoms or aromatic such as C.sub.6 H.sub.5, 
C.sub.6 H.sub.4 CH.sub.3, naphthyl; olefins such as 
trans-1,2-dichloroethylene; inorganic salts such as cyanides, isocyanates, 
thiocyanates, thiocyanides, sulfides, hydrosulfides and iodides wherein 
the metals are sodium or potassium; and hydrogen sulfide as well as any 
mixtures thereof. A preferred second complexing agent is a solution of 
acetic acid and pyridine in a weight ratio of from about 7:1 to about 4:1 
and most preferably of from about 6:1 to about 5:1. 
Previously employed methods for catalyst removal have dealt with 
coagulation of the polymer solution in dilute aqueous inorganic acid 
and/or addition of polar organic solvents such as alcohols, ketones, or 
hot water/steam. When this approach was tried in the present invention, 
the product obtained still contained appreciable quantities of catalyst 
resulting in poor heat aging and high oil swell. The use of dilute aqueous 
inorganic acids for the present invention resulted in a product with 
embrittlement and partial loss of the product in the aqueous acid 
solution. 
EXAMPLE 6 
Under nitrogen, 100 grams of the product of Example 1 was dissolved in 
several portions in one-half gallon of dry tetrahydrofuran in a one gallon 
high pressure reactor equipped with a paddle stirrer. The copolymer was 
completely dissolved in about four hours. 
Preparation of the hydrogenation catalyst solution 
Under nitrogen, a solution of 8.3 grams (12 weight percent) of cobalt (II) 
neodecanoate in mineral spirits and 17.5 grams hexamethylphosphoric 
triamide was prepared and cooled by means of an ice bath to about 
3.degree. C. To this purple solution was added, drop-wise, 26.7 grams (25 
weight percent, 1.9 molar solution) triethyl-aluminum catalyst in toluene. 
Evolution of gases occurred and the purple solution turned brown upon the 
addition of the triethylaluminum catalyst. After the addition of the 
triethylaluminum catalyst solution, a hydrogenation catalyst solution was 
stirred under nitrogen for one hour at room temperature. 
The hydrogenation catalyst was then added slowly to the stirred copolymer 
solution under nitrogen followed by the introduction of hydrogen (500 
psi). Periodically, the reactor was repressurized to 500 psi in order to 
compensate for hydrogen uptake by the polymer. When hydrogen uptake at 
room temperature ceased, the polymer solution was heated to 50.degree. C. 
and the hydrogen pressure increased to 1000 psi. Again, represurization 
was continued to compensate for hydrogen uptake by the polymer. After a 
total time of about six hours, hydrogen uptake stopped. The polymer 
solution was then cooled to room temperature. Excess hydrogen was vented 
and replaced with a nitrogen blanket. A solution of glacial acetic acid 
(200 grams) and pyridine (40 grams), deoxygenated by bubbling in nitrogen 
was then added under nitrogen to the polymer solution. After stirring for 
one hour at room temperature, the polymer solution was coagulated in hot 
(70.degree. C.) water, filtered and dried in air (100.degree. C., four 
hours), followed by drying in vacuum (80.degree. C., 1 mm Hg, two hours). 
The action of acetic acid/pyridine solution on the cobalt ions under 
anaerobic conditions was important in rendering the residual cobalt 
catalyst (intimately mixed in with the polymer) innocuous to polymer 
degradation. Without the acetic acid treatment, the hydrogenated polymer 
exhibits poor heat aging and high oil swell in hydrocarbon oils. When 
acetic acid/pyridine solution is added to the solution of the hydrogenated 
polymer in the presence of air, prior to polymer coagulation, heat aging 
is not improved. 
The hydrogenated random copolymer of Example 6 is compounded and evaluated 
in a side-by-side comparison with a nitrile rubber available from 
Nippon-Zeon having 36 weight percent acrylonitrile. The control Example 7 
and the invention Example 8 are both cured with sulfur. The evaluation is 
set out in Table III. All values are parts by weight. 
TABLE III 
______________________________________ 
Example 8 
Example 7 
Present 
Control Invention 
______________________________________ 
Stearic Acid 1 1 
Zinc Oxide 5 5 
Vanox ZMTI 2 2 
Nangard 445 2 2 
N550 Block 50 50 
Spider Sulfur .2 .2 
Methyl Tuads, TMTD 1.5 1.5 
Ethyl Tuads, TETD 1.5 1.5 
Santocure, CBTS 1.0 1.0 
Nippon-Zeon 100.00 
Nitrile Rubber 
Product of Example 6 100.00 
Rheometer (190.degree. C., 3.degree. Arc, 
100 cpm, Micro Die) 
ML (lbf. in) 10.0 5.1 
MHF (lbf. in) 58.6 38.6 
T.sub.s 2 (min.) 1.5 0.9 
T' 90 (min.) 2.7 1.7 
Cure Time (min.) 4.0 4.0 
Cure Time (min.) 6.0.sup.a 6.0.sup.a 
Original Properties (Cured at 190.degree. C.) 
Stress at 100% (psi) 383 383 
Stress at 200% (psi) 732 759 
Stress at 300% (psi) 1161 1234 
Tensile Strength (psi) 
2736 2939 
Elongation, Ultimate (%) 
850 788 
Hardness, Shore A (pts) 
71 70 
Compression Set (ASTM D395, 
90.1 85.1 
Method B, 70 hr. 150.degree. C.) 
Set (%) 
Gehman Low Temperature 
-26 -26 
Torsion Test 
Freeze Point (.degree. C.) 
ASTM #3 Oil (170 hr. 150.degree. C.) 
19 19 
Volume Change (%) 
Air Test Tube (70 hr. 175.degree. C.) 
Tensile, Ultimate (psi) 
2815 2792 
Tensile Change (%) 3 -5 
Elongation, Ultimate (%) 
399 386 
Elongation Change (%) 
-53 -51 
Hardness, Shore A (pts) 
80 80 
Hardness Change (pts) 
+9 +10 
______________________________________ 
.sup.a Tempered (4 hr, 177.degree. C.) 
The hydrogenated random copolymer of Example 6 is compounded and evaluated 
in a side-by-side comparison with a nitrile rubber available from 
Nippon/Zeon having 36 weight percent acrylonitrile. The control Example 9 
and the Invention Example 10 are both cured with peroxide. The evaluation 
is set out in Table IV. All values are parts by weight. 
TABLE IV 
______________________________________ 
EXAMPLE 10 
EXAMPLE 9 PRESENT 
CONTROL INVENTION 
______________________________________ 
Structol WB-222 2.0 2.0 
Stearic Acid 1.0 1.0 
AgeRite Stalite S 
2.0 2.0 
N550 Black 40.0 80.0 
Ricon 153D 4.0 4.0 
Vulcup 40KE 10.0 10.0 
Tetrono A 0.1 0.1 
Product of Example 6 
-- 100.0 
Nippon Zeon Nitrile Rubber 
100.0 -- 
Mooney Viscometer 
(125.degree. C. Large Rotor) 
Minimum Viscosity 
54.6 39.0 
T.sub.5 (min) &gt;35 &gt;35 
T.sub.35 (min) &gt;35 &gt;35 
Rheometer (190.degree. C., 3.degree. C. Arc, 
100 cpm, Micro Die) 
ML (lbf. in) 12.7 4.9 
MHF (lbf. in) 127.3 30.6 
T.sub.s 2 (min) 0.9 1.2 
T' 90 (min) 3.5 4.0 
Cure Time (min) 4.0 4.0 
Cure Time (min) 6.0 6.0 
(Compression Set Buttons) 
Cure Time (min) 4.0 4.0 
(Plied discs) 
Original Properties 
(Cured at 190.degree. C.) 
Stress at 100% (psi) 
650 550 
Stress at 300% (psi) 
-- 3100 
Tensile Strength (psi) 
3680 3500 
Elongation, Ultimate (%) 
300 350 
Hardness, Duro A (pts) 
70 69 
Gehman Low Temperature 
-30.7 -30.7 
Torsion Test 
Freeze pt. (.degree.C.) 
ASTM #3 Oil (70 hr. 150.degree. C.) 
Tensile, Ultimate (%) 
3125 3177 
Tensile Change (%) 
-15 -9 
Elongation, Ultimate (%) 
290 309 
Elongation Change (%) 
-3 -11 
Hardness, Shore A (pts) 
60 60 
Hardness Change (pts) 
-10 -9 
Volume Change (%) 
18 18 
Air Test Tube (70 hr. 175.degree. C.) 
Tensile, Ultimate (psi) 
1756 1789 
Tensile Change (%) 
-52 -49 
Elongation, Ultimate (%) 
108 112 
Elongation Change (%) 
-64 -68 
Hardness, Shore A (pts) 
75 75 
Hardness Change (pts) 
5 6 
______________________________________ 
While in accordance with the Patent Statutes, the best mode and preferred 
embodiment has been set forth, the scope of the invention is not limited 
thereto, but rather by the scope of the attached claims.