BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thermoplastic elastomer compositions based upon acrylate rubbers having improved stability toward elevated temperatures.

2. Description of Related Art Copolymers of ethylene with (meth) acrylates and a cure site monomer are well-known in the art. (As employed herein, the term" (meth) acrylate" is used for convenience to refer to both acrylates and methacrylates.) They have good high temperature durability, oil resistance, and low-temperature flexibility, which make them well suited to being vulcanized and used in automotive applications, such as powertrain seals and gaskets, rocker cover and piston seals, oil coolant hoses, power steering hoses, turbocharger hoses, crankcase ventilating tubes, coverings for fuel and coolant hoses, O-rings, grommets and spark plug boots. See http ://dupont. com/industrial-polymers/vamac/H-84302. html.

U. S. Patent Nos. 3,658,769 and 3,767,628 disclose amide and imide age resisters such as N- (4-anilinophenyl) acrylamide, N- (4-anilinophenyl) maleamic acid and N- (4- anilinophenyl) maleimide, age resistant polymers having amide and imide age resisters physically combined therewith and age resistant polymeric compositions prepared by free radical polymerization techniques involving the use of said amides and imides as monomers.

U. S. Patent No. 3,904,588 discloses random copolymers of ethylene, alkyl acrylate and 1,4-butene-dioic aced esters whose vulcanizates exhibit both low brittle point and low oil swell characteristics.

U. S. Patent No. 4,213,892 discloses that polymers are rendered more oxidatively stable by reaction with an antioxidant or stabilizer, generally a vinyl-group-or thiol group- containing antioxidant, in the presence of a free radical which may be produced by a redox system or ultra-violet light. The resulting polymers can be used as such or can be used as additives in other polymers to stabilize the latter.

U. S. Patent No. 4,275,180 discloses a polymer composition which comprises a crosslinkable or crosslinked blend of an elastomer and a thermoplastic polymer, the elastomer comprising a polymer of ethylene with an ethylenically unsaturated aliphatic ester, and the elastomer and the thermoplastic polymer being substantially free of halogen-containing substituents. The compositions are said to be useful as jacketing materials for wire and cable, as harnessing materials, and in the manufacture of heat recoverable articles having improved oil resistance and thermal ageing properties.

U. S. Patent No. 4,351,931 discloses high molecular weight uniformly random copolymers of ethylene and acrylic or methacrylic acid containing up to 10 weight percent of the acid.

U. S. Patent No. 4,634,615 discloses a heat recoverable tubular composite article comprising an inner layer comprising a crosslinked elastomeric polymeric material having a modulus at 100% elongation at 20° C. of about 40 to about 900 pounds per square inch and an outer layer comprising a thermoplastic material having a 2% secant modulus at 20° C. of about 5,000 to about 100,000 pounds per square inch said composite article (1) being formed by coextrusion, (2) having a direct bond between said layers with a peel strength of at least 6 pounds per linear inch, and (3) being in a radically expanded configuration, said thermoplastic outer layer being capable of retaining the elastomeric inner layer in an expanded configuration at ambient temperature and incapable of retaining the elastomeric layer in an expanded configuration at a temperature above a predetermined temperature thereby permitting the composite article to recover to or toward its unexpanded configuration.

U. S. Patent No. 4,654,402 discloses compatibilized polymer blends comprising a blend of olefin polymer, cross-linkable acrylic ester copolymer rubber, and a compatibilizing amount of a graft copolymer comprising acrylic ester copolymer compatibilizing segments and olefin polymer compatibilizing segments.

U. S. Patent No. 4,696,967 discloses a low smoke and flame retardant composition comprising an acrylate rubber and a polyolefin resin compatibilized with aluminum trihydrate. The composition can be made by dynamically partially curing blends of acrylate rubber and polyolefin resin with compatibilizing amounts of aluminum trihydrate to yield a thermoplastic elastomer said to have improved properties at elevated temperatures. The acrylate rubber can comprise an acrylate ester polymer or a copolymer of acrylate ester with ethylene. The polyolefin resin is preferably a high molecular weight polymerization product of either ethylene or propylene, preferably propylene.

U. S. Patent No. 4,769,179 discloses a flame-retardant resin composition comprising (A) about 100 parts by weight of at least one resin selected from the group consisting of ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, isobutylene-isoprene copolymer and ethylene-propylene-diene terpolymer, (B) about 50 to about 300 parts by weight of a hydrate of metallic oxide, and (C) about 0.05 to about 5 parts by weight of a phosphorus-containing titanate coupling agent, the composition having been already crosslinked by use of about 0.1 to about 20 parts by weight of a crosslinking agent or by irradiation of ionizable radiation.

U. S. Patent No. 4,882, 388 discloses a rubber composition said to have a good balance among low temperature resistance, oil resistance, heat aging resistance, and mechanical strength characteristics. This rubber composition comprises a rubber component composed of an ethylenic copolymer rubber and an acrylic rubber, wherein the ethylenic copolymer rubber is a copolymer comprising (a) 50 to 85% by mole of ethylene, (b) 50 to 15% by mole of an acrylate and/or a methacrylate, and (c) 0.05 to 8% by mole, based on the total of said components (a) and (b), of a cross-linked point forming monomer; and the acrylic rubber contains at least 60% by mole of at least one monomer selected from among at least an alkyl acrylate, an alkyl methacrylate and an alkoxyalkyl acrylate.

U. S. Patent No. 5,028,674 discloses an improvement in a process for the continuous copolymerization of ethylene with certain polar comonomers having reactive double bonds, wherein a single phase is maintained in the reactor by means of methanol introduced concurrently with the reactants, whereby reactor fouling is significantly reduced or eliminated.

U. S. Patent No. 5,053,450 discloses compositions of acrylic rubber and another rubber which can be nitrile rubber, hydrogenated nitrile rubber, fluoroelastomer, silicone rubber, or fluorosilicone rubber, in which the acrylic rubber is at least partially crosslinked. The compositions are said to be millable and processable and, by the addition of curatives for the nitrile rubber, hydrogenated nitrile rubber, fluoroelastomer, silicone rubber, or fluorosilicone rubber, can be further crosslinked to become vulcanizates which are said to exhibit excellent resistance to the effects of hot air, hot oil, and ozone.

U. S. Patent No. 5,073,592 discloses a process for preparing a rubber containing polymer bound antidegradants. The process comprises the aqueous emulsion polymerization of (a) at least one functionalized monomer that contains an antidegradant moiety and a polymerizable vinyl group; with (b) at least one copolymerizable conjugated diene monomer, wherein the polymerization is conducted in the presence of from about 1 to about 70 parts by weight of an ester based on 100 parts by weight of total monomers. The ester functions as a synergist for the antidegradant, as a cosolvent/dispersing agent for the antidegradant during emulsion polymerization and as a plasticizer for the final polymer product.

U. S. Patent No. 5,075,383 discloses an additive composition comprising a graft and amine-derivatized copolymer prepared from ethylene and at least one C3 to Clo alpha- monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of said C3 to Clo alpha-monoolefin and from about 0 to 15 mole percent of said polyene, said copolymer having a number average molecular weight ranging from about 5,500 to 50,000 and having grafted thereon at least 1.8 molecules of a carboxylic acid acylating function per molecule of said copolymer and reacting said grafted copolymer with an amino-aromatic polyamine compound from the group consisting of an N-arylphenylenediamine, an aminocarbazole, an aminoindole, an amino-indazolinone, an aminomercaptotriazole, and an amino-perimidine to form said graft and amine-derivatized copolymer, and a lubricating oil composition containing same.

U. S. Patent No. 5,085,905 discloses an elastomeric composition, said to have improved adhesion to metal reinforcement, comprising an elastomer containing, an adhesion promoting amount of a polysulfide having the formula R--S (,--R'where m is an integer of from about 2 to 6; R and R'are the same or different and are certain structurally defined moieties, each containing at least one tertiary amine group, or are a monoalkylated phenol wherein the alkyl group contains from about 1 to 4 carbon atoms.

U. S. Patent No. 5,182,041 discloses an additive composition comprising a graft and amine-derivatized polymer having an average molecular weight ranging from about 300 to 3500 which has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates characterized by having a carboxylic acid acylating function within their structure and reacting said reaction intermediate with an amino-aromatic polyamine compound from the group consisting of an N- arylphenylenediamine, an aminothiazole, an aminocarbazole, an amino-indazolinone, an aminomercaptotriazole and an aminoperimidine to form said graft and amine-derivatized copolymer, and a lubricating oil composition containing same.

U. S. Patent No. 5,216,049 discloses an antidegradant system comprised of (A) an antidegradant selected from the group consisting of phenolic antidegradants, amine antidegradants and mixtures thereof ; and (B) a unique polymerizable synergist. In addition, there is disclosed a stabilized polymer comprising (A) a polymer selected from the group consisting of (1) homopolymers and copolymers of monoolefins ; (2) natural rubber; and (3) synthetic rubber derived from a diene monomer; (B) from about 0.05 to about 10 parts by weight based upon 100 parts of polymer of an antidegradant selected from the group consisting of phenolic antidegradants, amine antidegradants and mixtures thereof; and (C) from about 0.05 to about 20 parts by weight based upon 100 parts of polymer of a unique polymerizable aromatic sulfide synergist.

U. S. Patent No. 5,250,627 discloses a rubber composition which comprises the following components (A) and (B): (A) an ethylene copolymer rubber comprising ethylene and at least one compound selected from the group consisting of acrylic esters and methacrylic esters as constituting units, and (B) a hydrogenated unsaturated nitrile-conjugated diene copolymer rubber. This composition is said to be well balanced in its properties such as strength characteristics, oil resistance, low- temperature resistance and ozone resistance.

U. S. Patent No. 5, 250,644 discloses a crosslinkable acrylic rubber said to have good alkali resistance and oil resistance as well as other properties required generally for acrylic rubber, which is prepared by copolymerization of an alkyl acrylate and 0.2 to 15 parts by weight, per 100 parts by weight of the alkyl acrylate, of a partial ester of an unsaturated polycarboxylic acid having n carboxyl groups wherein n is an integer of not less than 2 and n- 1 carboxyl groups are esterified.

U. S. Patent No. 5,284,906 discloses a process for preparing a rubber containing polymer bound functionalities. The process comprises the emulsion polymerization at a temperature ranging from about 0° C. to about 25° C. of (a) at least one functionalized monomer that contains a polymerizable vinyl group; with (b) at least one copolymerizable conjugated diene monomer selected from the group consisting of butadiene 1,3,2- chlorobutadiene-1,3, isoprene, piperylene and conjugated hexadienes; wherein the polymerization is conducted in the presence of from (1) from 2 to 30 parts by weight of an ionic surfactant per 100 parts by weight of organic components and (2) about 1 to about 70 parts by weight of a plasticizer based on 100 parts by weight of total monomers.

U. S. Patent No. 5,284,907 discloses a process for preparing a masterbatch rubber containing polymer bound functionalized moieties. The process comprises the emulsion polymerization at a temperature from 40 ° C. to 100 ° C. of (a) at least one functionalized monomer that contains a polymerizable vinyl group; with (b) at least one copolymerizable conjugated diene monomer selected from the group consisting of butadiene-1, 3,2 chlorobutadiene-1,3, isoprene, piperylene and conjugated hexadienes, wherein the polymerization is conducted in the presence of from (1) from 2 to 30 parts by weight of an ionic surfactant per 100 parts by weight of organic components and (2) about 10 to about 70 parts by weight of a plasticizer based on 100 parts by weight of total monomers.

U. S. Patent No. 5,504,167 discloses an improved process for the continuous copolymerization of ethylene with certain polar comonomers having reactive double bonds wherein reactor fouling is significantly reduced or eliminated by use of surfactants.

U. S. Patent No. 5,578,681 discloses curable elastomeric blends of fluoroelastomer and ethylene copolymer elastomer in which at least one of the fluoroelastomer and ethylene copolymer elastomer contains a cure site monomer.

U. S. Patent No. 6,035,899 discloses a fiber-reinforced rubber hose having an inner tubular portion made of a first rubber; an outer tubular portion which is made of a second rubber and surrounds the inner tubular portion; and a reinforcing layer interposed between the inner and outer tubular portions. At least one of the first and second rubbers is a carboxyl- containing acrylic elastomer prepared by vulcanizing a carboxyl-containing acrylic copolymer. The reinforcing layer is prepared from polyester fibers containing terminal carboxyl groups which are in an amount of up to 20 equivalents per metric ton of the polyester fibers. The rubber hose is said to be superior in metal contact resistance and calcium chloride resistance, in addition to satisfactory heat resistance, oil resistance, pressure resistance and sealing capability.

Parker et al., in Rubber Chemistry and Technology, 62 (4) : 732-749 (1989), describe the copolymerization of styrene, butadiene, and N- (4-anilinophenyl)-methacrylamide to form an SBR rubber having a polymer-bound antioxidant.

The disclosures of the foregoing are incorporated herein by reference in their entirety.

Recently, articles used in various industrial fields such as automobiles, appliances, and machines have been required to provide high performance and functions and have been used under increasingly severe conditions. This tendency is especially pronounced in the automobile industry, which is the largest user of rubbers. For example, the atmosphere in engine compartments tends to be higher in temperature owing to countermeasures against regulation of exhaust or improvement of engines aimed at enhancement of performance, such as increased power output, and rubbers to be employed for such uses are required to be excellent not only in heat resistance, ozone resistance, and oil resistance, but also in flexibility at low temperatures ; that is to say, to be well balanced in properties.

In accordance with the foregoing, owing to the increased demands of conditions existing in modern automotive systems, there is a need for copolymers of ethylene, (meth) acrylates, and a cure site monomer that have improved stability at high temperatures.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method for increasing the temperature stability of copolymers of ethylene, (meth) acrylates, and a cure site monomer by grafting an aromatic amine onto the cure site monomer. More particularly, the aromatic amine is a sterically unhindered primary amine.

In a preferred embodiment, the present invention is directed to a method for increasing the temperature stability of a copolymer comprising ethylene, at least one (meth) acrylate, and at least one a, P-ethylenically unsaturated mono-or polycarboxylic monomer comprising grafting onto said copolymer an aromatic amine having a single primary amine group in a sterically unhindered position on the molecule.

In another aspect, the present invention is directed to a copolymer derivative having improved temperature stability, as compared to the underivatized copolymer, prepared by grafting onto said underivatized copolymer an aromatic amine having a single primary amine group in a sterically unhindered position on the molecule, wherein said copolymer comprises ethylene, at least one (meth) acrylate, and at least one a, P-ethylenically unsaturated mono-or polycarboxylic monomer.

In still another aspect, the present invention is directed to an elastomer prepared by the vulcanization of a copolymer derivative having improved temperature stability, as compared to the underivatized copolymer, said derivative having been prepared by grafting onto said underivatized copolymer an aromatic amine having a single primary amine group in a sterically unhindered position on the molecule, wherein said underivatized copolymer comprises ethylene, at least one (meth) acrylate, and at least one a, P-ethylenically unsaturated mono-or polycarboxylic monomer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The elastomeric ethylene copolymers used in this invention are polyamine-curable or peroxide-curable copolymers of ethylene, at least one (meth) acrylate, and at least one other monomer that is a cure site monomer. The cure site monomer (s) comprise a, (3-unsaturated carboxylic acids, preferably of 3-12 carbon atoms, selected from the group consisting of monocarboxylic acids, polycarboxylic acids, and acid esters of polycarboxylic acids. These additional monomers render the ethylene copolymer elastomer reactive with the aromatic amines employed in the practice of the present invention, as well as polyamine-curable, if such curing is desired. Such copolymers are well-known in the art and a large number of such copolymers are available commercially.

The ethylene content of the copolymers can be in the range of from about 20 to about 65 weight percent of the polymer. Preferably it is from about 20 to about 55 weight percent, more preferably from about 20 to about 45 weight percent.

The alkyl (meth) acrylate comonomer (s) comprise about 45-75 wt % of the copolymer, preferably about 50-75 wt %. Alkyl (meth) acrylates suitable for use in the copolymers include Cl-C8 alkyl esters of (meth) acrylic acid, for example, the methyl, ethyl, propyl, butyl, hexyl, heptyl, and octyl esters, including isomers thereof, e. g., isobutyl, 2-ethyl hexyl, and the like. Methyl, ethyl, and butyl acrylates are preferred. Methyl acrylate is most preferred.

The a, (3-unsaturated mono-or polycarboxylic acids are present in an amount sufficient to provide from about 0.1 to about 10 wt %, preferably 0.5-5.0 wt % of carboxylate groups. Suitable a, ß-unsaturated mono-or polycarboxylic acids include those having 3-12 carbon atoms, for example, monocarboxylic acids such as acrylic acid, methacrylic acid, and ethacrylic acid ; dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid ; monoesters of dicarboxylic acids such as ethyl hydrogen maleate, ethyl hydrogen fumarate, and 2-ethylhexyl hydrogen maleate; tricarboxylic acids such aconitic acid; and diesters of tricarboxylic acids such as dimethyl aconitate, diethyl aconitate, and methyletliyl aconitate.

Unsaturated epoxy group-containing monomers, e. g., glycidyl esters, such as glycidyl acrylate, glycidyl methacrylate, diglycidyl itaconate, trigylcidyl butenetricarboxylate, and glycidyl p-styrenecarboxylate, can also be employed. The acids may be used alone or in combination. Acrylic acid, methacrylic acid, and ethyl hydrogen maleate are preferred.

If desired, additional monomers may be copolymerized with the above-described monomers, e. g., isobutylene, styrene and derivatives thereof, and halogenated polyolefins, such as tetrafluoroethylene and hexafluoropropylene.

Such copolymers are generally prepared by continuous copolymerization of ethylene and the comonomers in a stirred reactor in the presence of at least one free-radical initiator at temperatures of from about 120° C to about 300° C and at pressures of from about 130 to about 310 MPa. The most effective initiators have half lives of 0.1-1.0 sec at the reactor temperature, for example, lauryl peroxide, di-t-butyl peroxide, t-butyl peracetate, di (sec- butyl) peroxy dicarbonate, t-butyl peroxy neodecanoate, and t-amyl peroxy pivalate.

Optionally, the copolymers can be prepared in the presence of about 2-25 wt % methanol or acetone so that reactor fouling is decreased or eliminated, as disclosed in U. S. Patent No.

5,028,674 and U. S. Patent No. 5,027,593. Following discharge of polymer from the reactor, viscosity can be increased by subjecting the polymer to post-reactor processing as disclosed, for example, in U. S. Patent No. 5,194,516 and U. S. Patent No. 5,214,108. The disclosures of these patents are incorporated herein by reference in their entirety.

Representative examples of specific ethylene copolymers which can be used in the present invention include ethylene/butyl acrylate/carbon monoxide, ethylene/butyl aciylate/glycidyl methacrylate, ethylene/butyl acrylate/acrylic acid, ethylene/methyl acrylate/carbon monoxide, ethylene/butyl acrylate/carbon monoxide, ethylene/methyl acrylate/ethyl hydrogen maleate, ethylene/methyl acrylate/methacrylic acid, ethylene/butyl acrylate/acrylic acid, ethylene/fumaric acid/methyl acrylate, ethylene/ethyl hydrogen maleate/carbon monoxide/methyl acrylate, ethylene/methacrylic acid/carbon monoxide/vinyl acetate, and ethylene/ethyl hydrogen maleate/carbon monoxide/vinyl acetate. Preferably, the copolymers contain copolymerized units of Cl-C8 alkyl (meth) acrylates. VAMAC (§) G, commercially available from E. I. Du Pont de Nemours and Company, is especially preferred.

It is understood to be a terpolymer comprising 41% ethylene, 55% methyl acrylate, and 4% maleic acid monoethyl ester. See U. S. Patent No. 5,504,167.

In accordance with the present invention, the a, P-unsaturated mono-or polycarboxylic acid, i. e., the cure site monomer, has grafted thereto an aromatic amine. The aromatic amine is preferably selected from the group consisting of : a) an N-aryl phenylenepolyamine represented by the formula: in which Ar is aromatic, R'is H,-NHaryl,-NHarylalkyl, a branched or straight chain radical having from 4 to 24 carbon atoms that can be allcyl, alkenyl, alkoxyl, aralkyl, alkaryl, hydroxyalkyl or aminoalkyl, W and R3 are H, NH2, (NH (CH2) n) mNH27 CH2 (CH2) nNH2, or CH2-aryl-NH2, in which n and m are independently selected integers of from 1 to 10, provided that one and only one of R2 and R3 is hydrogen; b) an aminothiazole selected from the group consisting of aminothiazole, aminobenzothiazole, aminobenzothiadiazole, and aminoalkylthiazole, c) an aminocarbazole represented by the formula : in which R and R'are independentyl selected from the group consisting of hydrogen or an alkyl or alkenyl, radical having from 1 to 14 carbon atoms, and one of R2 and R3 is hydrogen and the other is NH2,-(NH (CH2) n) mNH2,-CH2 (CH2) nNH2, or-CH2-aryl-NH2, in which n and m are independently selected integers of from 1 to 10, provided that the NH2 moiety of R2 or R3 is not in a position to be sterically hindered by R' ; d) an amino-indazolinone represented by the formula: in which Rl is hydrogen or an alkyl radical having from 1 to 14 carbon atoms, and one of R2 and R3 is hydrogen and the other is NH2,- (NH(CH2)n)mNH2, -CH2(CH2)nNH2, or -CH2-aryl-NH2, in which n and m are independently selected integers of from 1 to 10, provided that the NH2 moiety of R2 or R3 is not in a position to be sterically hindered by R' ; (e) an aminoindole represented by the formula: in which Rl is hydrogen or an alkyl radical having from 1 to 14 carbon atoms, and one of R' and R3 is hydrogen and the other is NH2,- (NH(CH2)n)mNH2, -CH2(CH2)nNH2, or CH2-aryl-NH2, in which n and m are independently selected integers of from 1 to 10, provided that the NH2 moiety of R2 or R3 is not in a position to be sterically hindered by Rl ; (f) an aminomercaptotriazole represented by the formula: and (g) an aminoperimidine represented by the formula : in which Ri represents hydrogen or an alkyl radical having from 1 to 14 carbon atoms.

Preferably, the aromatic amine is an N-phenyl-phenylenediamine represented by the formula : wherein Rl is H,-NHaryl,-NHarylalkyl, a branched or straight chain radical having from 4 to 24 carbon atoms that can be alkyl, alkenyl, alkoxyl, aralkyl, alkaryl, hydroxyalkyl or aminoalkyl, R'and R'are H, NH2,- (NH (CH2) n) mNH2,-CH2 (CH2) nNH2, or-CH2-aryl-NH2, in which n and m are independently selected integers of from 1 to 10, provided that one and only one of W and R3 is hydrogen. More preferably, W is hydrogen. Most preferably, R3 is NH2.

Bis-a-methylstyryldiphenylamine is well-know in the art as a particularly advantageous antioxidant for use with VAMAC polymers. In a preferred embodiment of the present invention, bis-a-methylstyryldiphenylamine is used in combination with one or more of the above described aromatic amines. It is especially preferred that it be used with N- phenyl phenylenediamine in the practice of the present invention.

Various features and aspects of the present invention are illustrated further in the examples that follow. While these examples are presented to show one skilled in the art how to operate within the scope of the invention, they are not intended in any way to serve as a limitation upon the scope of the invention.

EXAMPLES Example 1 N-phenyl phenylenediamine was grafted onto VAMAC G (a terpolymer understood to comprise 41 wt % ethylene, 55 wt % methyl acrylate, and 4 wt % maleic acid monoethyl ester) at 1%, 2%, and 4% levels by reaction of the primary amino group of the diamine with the carboxylic acid group of the maleic acid monoethyl ester in the presence of stearic acid.

Seven experimental samples were prepared, the details of which are shown in Table 1. Table1 Grafting of N-Phenyl Phenylenediamine onto VAMAC G A B C D E F G VAMAC G 70 g 66. 9 g 66. 8 g 67. 6 g 66.5 g 67. 5 g 67. 5 g Stearic Acid-1. 00 g 1. 01 g 1. 01 g 1. 02g 1. 01 g 1. 01 g N-phenyl phenylenedianzine T 0. 67 g 1.33 g 1 2.66g 1.33g 1. 33g For Examples A through E, the reaction was carried out by mixing the components in a Brabender mixing head (@ 30 rpm) at 105° C. under nitrogen for thirty minutes. Example F was compounded in a Brabender mixing head (@ 30 rpm) at 105° C. in air for thirty minutes. Example G was compounded in a Brabender mixing head (@ 30 rpm) at 90 ° C. in air for three minutes.

Grafting was confirmed by extracting 20 grams of each of Examples A through E of the reacted VAMAC G polymers with refluxing toluene for 18 hours or more. Additionally, 20 grams of each of Examples A through G were extracted with refluxing isopropyl alcohol (IPA) for 40 hours. The extracted polymers were tested by the Oxidation Induction Time (OIT) test and compared to the corresponding non-extracted polymer.

Antioxidant properties of a product in a fully formulated plastic are determined in the Oxidation Induction Time (OIT) test under ASTM D3895 conditions. The test is performed at a suitable temperature for a given plastic, here 225 ° C. Circular disks are cut from 0.25 mm films of the material to be tested and placed in aluminum pans for use in a Perkin-Elmer DSC-2C differential scanning calorimeter (DSC). The test chamber of the DSC calorimeter is purged with nitrogen during conditioning to an isocratic temperature at 225° C.

Conditioning is followed by immediate change to oxygen at a flow rate of 20 cc's per minute to induce thermal oxidative degradation. OIT is the time span in minutes between reaching an isocratic temperature when the oxygen environment is introduced and the time at which the DSC detects the onset of oxidation. The OIT test measures the resistance to oxidation of a polymer or material and a greater value is more desired.

The results show that after extraction the 1 % grafted material retains 84% of non- extracted OIT (@ 225 ° C). The 2% and 4% grafted materials retain 89% and 68% of non- extracted OIT (@ 225 ° C), respectively. See Table 2.

Table 2 Oxidative Induction Times Method: OIT 225 ° C., 700 minutes, Auto Term @ 2 Sample Run 1 Run 2 Average A 0.34 0.34 0 B 0.31 0.36 0 C 136.16 143.03 140 D 203.32 184.78 194 E 276.83 291.91 284 F 221.29 217.6 219 G 200.26 197.57 199 A Extracted with Toluene 0.36 0.33 0 B Extracted with Toluene 0.31 0.30 0 C Extracted with Toluene 119.53 116.47 118 D Extracted with Toluene 165.76 163. 51 165 E Extracted with Toluene 195.44 194.21 195 A Extracted with IPA 0. 31 0.3 0 B Extracted with IPA 0.3 0.32 0 C Extracted with IPA 48.64 47.89 48 D Extracted with IPA 115.07 113.07 114 E Extracted with IPA 164.6 163.6 164 F Extracted with IPA 155.32 145.62 141 G Extracted with IPA 123.26 112.79 118 These results clearly indicate that grafting the antioxidant onto the polymer chain greatly increases the OIT of the polymer.

Example 2 N-phenyl phenylenediamine was grafted onto VAMAC G (a terpolymer understood to comprise 41 wt % ethylene, 55 wt % methyl acrylate, and 4 wt % maleic acid monoethyl ester) at 1%, 2%, and 4% levels by reaction of the primary amino group of the diamine with the carboxylic acid group of the maleic acid monoethyl ester in the presence of stearic acid.

Four experimental samples were prepared, the details of which are shown in Table 3.

Table 3 A (Control) B C D VAMAC G (Base Polymer) 100.0 100.0 100.0 100.0 N550 Black (Carbon Black) 80.0 80.0 80.0 80.0 Armeen 18D (Release Agent) 0.5 0.5 0.5 0.5 VANFRE VAM (Release Agent) 1.0 1.0 1.0 1.0 Stearic Acid (Release Agent) 1.5 1.5 1.5 1.5 PLASTHALL 670 (Plasticizer) 10.0 10.0 10.0 10.0 DIAK#1 (Accelerator) 1.25 1.25 1.25 1.25 DOTG (Vulcanizing Agent) 4.0 4.0 4.0 4.0 NAUGARD 445 (Antioxidant)--2. 0--2. 0 N-phenyl phenylenediamine--2. 0 2.0 Naugard 445 (Uniroyal Chemical Co.) is 4,4'-bis (M, M dimethyl) diphenylamine.

The results of tensile testing of these compositions, unaged and aged for 1000 hours at 175° C are shown in Table 4.

Table 4 Unaged A B C D Tensile at brealc, psi 2250 2140 1890 1790 Elongation at break, % 230 250 300 300 Aged 1000 hours at 175° C Tensile at break, psi 1890 1800 2260 1990 Elongation at brealc, % 20 40 40 30 These results show that the compositions comprising the grafted N-phenyl phenylenediamine according to the present invention have the same heat resistance as those having 4,4'-bis (, No dimethyl) diphenylamine added separately, but N-phenyl phenylenediamine grafted onto the polymer is less extractable, which is critical in automotive applications.

In view of the many changes and modifications that can be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection to be afforded the invention.