WO1999024506A1

WO1999024506A1 - Partially cured thermoplastic elastomers of olefin rubber and polyolefin resin

Info

Publication number: WO1999024506A1
Application number: PCT/US1998/021829
Authority: WO
Inventors: Henno August Petersen; Timothy John Davies
Original assignee: Uniroyal Chemical Company, Inc.
Priority date: 1997-11-10
Filing date: 1998-10-15
Publication date: 1999-05-20

Abstract

A composition and process of making partially cured thermoplastic elastomers of olefin rubber and polyolefin resins where the rubber is partially cured with a peroxide curative and a N,N'-m-phenylenedimaleimide coagent. The tensile strength and compression set are improved.

Description

PARTIALLY CURED THERMOPLASTIC ELASTOMERS

OF OLEFIN RUBBER AND POLYOLEFIN RESIN

Background of the Invention This invention is directed to thermoplastic elastomer blends with certain improved properties. More specifically, it relates to thermoplastic elastomer blends partially peroxide cured by dynamic vulcanization with improved compression set and high tensile strength.

Background of the Prior Art The properties of compression set and tensile strength are important to the rubber industry and end users of their products. Compression set may be defined as a permanent deformation resulting from compressive stress, or the ability of a material to resist a crushing stress. It therefore follows that a lower value for compression set is desirable, as this is indicative of the material having a better recovery from deformation. A related physical property, tensile strength, is the maximum tensile stress (stretching) that may be sustained by the system. It is also a measure of when the material fails in tension.

Dynamically vulcanized blends of monoolefin copolymers and polyolefin resins are known. In, for example, USP 3,806,558 and Re. 31,518, both by Fischer, these type of materials are disclosed. Thermoplastic elastomers can be processed and fabricated by usual methods in which the vulcanization is not required for the development of elastomeric properties. Blends of monoolefin copolymers with polyolefins have also been known but such blends have not had the desirable physical strength characteristics of thermoplastic elastomers in terms of compression set in the above two examples of prior activity.

Improved compression set in fully cured, dynamically vulcanized blends of olefin rubber and polyolefin resin is described in U.S. Patent 4,311,628 to Abdou- Sabet, et al. The compositions mentioned therein were fully cured with phenolic resin. In U.S. Patent 4,130,535 to Coran, et al fully cured, dynamically vulcanized blends of olefin rubber and polyolefin resin were also described using an organic peroxide and N.N'-m-phenylenedimaleimide (in Examples 31-34). Improved compression set of this invention are not demonstrated for these fully cured materials. In the instant invention, the rubber is only partially cured. It is an object of the present invention to disclose thermoplastic elastomer blends partially cured by dynamic vulcanization with improved compression set and high tensile strength. It is a further object of this invention to provide finished rubber articles which do not require a time consuming vulcanization step in order to develop good physical properties. A still further object relates to a method of preparing such a thermoplastic elastomer blend, comprising dynamically partially curing a mixture of monoolefin copolymer rubber and polyolefin resin such as polyethylene or polypropylene.

These objects, as well as additional objects, will be presented herein.

Summary of the Invention

The present invention relates to a dynamically partially cured blend of monoolefin copolymer rubber and polyolefin resin, such as polyethylene or polypropylene. Such a blend is thermoplastic and can be fabricated into useful articles by conventional plastics processing methods. Examples of such methods include injection molding or extrusion, and the present invention relates to the manufacture of such articles.

As they are akin to many typical thermoplastic materials, the blends of the present invention may be reprocessed. They do not require a time consuming vulcanization step in order to develop good physical properties. The present invention also relates to a method of preparing a thermoplastic elastomeric blend, comprising dynamically partially curing a mixture of monoolefin copolymer rubber and polyolefin resin such as polyethylene or polypropylene. The present invention also relates to thermoplastic elastomers prepared according to this method. Detailed Description of The Invention

In this invention, dynamic or dynamically partially curing means that the materials comprising a mixture are masticated or sheared in an internal mixer or on a roll mill, while being subjected to curing conditions. In this invention, the cure imparted under these dynamic conditions is only partial. By this is meant that the blend does not become crosslinked to the extent that it will no longer hold together in a coherent mass in conventional rubber, or plastics processing equipment.

Any of the numerous well known chemical curing agents may be added during the dynamic partial curing process. Such agents are well-known to those familiar with the industry and may include any conventional curative. Typical materials include but are not limited to free radical generating agents or crosslinking agents such as the peroxides, whether aromatic or aliphatic as exemplified by the aromatic diacyl peroxides and aliphatic diacyl peroxides, dibasic acid peroxides, ketone peroxides, alkyl peroxyesters, alkyl hydroperoxides, including diacetylperoxide, dibenzoyl peroxide, bis-2,4-dichloro benzoyl peroxide, di-t-butyl peroxide, dicumylperoxide, t- butylperbenzoate, t-butylcumyl peroxide, 2,5-bis (t-butylperoxy)-2,5-dimethylhexane, 2,5-bis (t-butylperoxy)-2,5-dimethylhexyne-3, 4,4,4',4'-tetra(t-butylperoxy)-2,2- dicyclohexylpropane, 1 ,4-bis-(t-butyl)-peroxy-isopropylbenzene, 1 , 1 -bis-(t- butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butyl-peroxy) hexane, lauroyl peroxide, succinic acid peroxide, cyclohexanone peroxide, t-butyl peracetate, butyl hydroperoxide, and the like.

Less desired optional additional curatives are the azide types of curing agents. These may be useful as auxiliary curatives so long as they are used in amounts insufficient to fully cure the rubber of the blends. These include the azido formates (e.g. tetramethylenebis azidoformate), aromatic polyazides (e.g. 4,4'-diphenylmethane diazide), and sulfonazides (e.g. p,p'-oxybis (benzene sulfonyl azide). Other curatives that may be used include the aldehydeamine reaction products such as formaldehyde- ammonia, formaldehyde-ethylchloride-arnmonia, acetaldehyde-ammonia, formaldehyde-aniline, butyraldehyde-aniline, heptaldehyde-aniline, heptaldehyde- formaldehyde-aniline, hexamethylenetetramine, α-ethyl-β-propylacrolein-aniline; the substituted ureas such as trimethylthiourea, diethylthiourea, dibutylthiourea, tripentylthiourea, 1 ,3-bis (benzothiazolyl-mercaptomethyl) urea, and N,N- diphenylthiourea; guanidines such as diphenylguanidine, di-o-tolylguanidine, diphenylguanidine phthalate, and di-o-tolylguanidine salt of dicatechol borate; xanthates such as zinc ethylxanthate, sodium isopropylxanthate, butylxanthic disulfide, potassium isopropylxanthate, and zinc butylxanthate; dithiocarbamates such as copper dimethyl-, zinc dimethyl-, tellurium diethyl-, cadmium dicyclohexyl-, lead dimethyl-, selenium dibutyl-, zinc pcntamethylene-, zinc didecyl- and zinc isopropyl- octyl dithiocarbmate; thiazoles, such as 2-mercaptobenzothiazole, zinc mercaptothiazolyl mercaptide, 2-benzothiazolyl-N,N-diethylthiocarbamyl sulfide, and

2,2'-dithiobisbenzothiazole; imidazoles such as 2-mercaptoimidazoline and 2- mercapto-4,4,6-trimethyl-dihydroxypyrimidine; sulfenamides such as N-t-butyl-2- benzothiazole-, N-cyclohexylbenzothiazole-, N,N-diisopropylbenzothiazole-, N-(2,6- dimethylmorpholino)-2-bcnzothiazole-, and N,N-diethylbenzothiazole-sulfenamide; thiuramdisulfides such as N,N'-diethyl-, tetrabutyl-, N,N'-diisopropyldioctyl-, tetramethyl-, N,N'-dicyclohexyl-, and N,N'-tetralaurylthiuramdisulfide. Also to be considered are paraquinonedioxime, dibenzoparaquinonedioxime, and the like as well as sulfur itself. Other such peroxy compounds maybe found in reference books used by practitioners in the rubber industry such as the Encyclopedia of Chemical Technology and Organic Peroxides, published by Wiley-Interscience.

In the present invention, the organic peroxy curative is combined with the coagent N,N'-m-phenylenedimaleimide. The combination of these two agents results in a partially cured blend which has significantly lower compression set and higher tensile strength than is obtained with the peroxide curative alone. The material with improved compression set from the coagent and peroxide cure system of the instant invention is thermoplastic, not thermoset. The difference between these classes of materials are marked; thermoset materials undergo a chemical change when heated and are incapable of continuous inelastic deformation without chemical decomposition, thermoplastic materials become soft and malleable upon heating and become rigid again upon cooling without appreciable chemical change. Due to these very basic differences, compression set properties are not readily transferable from one class to the other. It is therefore surprising that a material that improves compression set in a thermoset material does the same in a thermoplastic. Even more surprisingly, N,N'-m-phenylenedimaleimide has been reported to cause a significant decrease (26% and 15% decrease from original) in tensile strength when it is used as a coagent for peroxide cures. As will be seen from the tabulated data evaluating the compounds made by the process of this invention, a significant increase in tensile strength was seen. The monoolefin copolymer rubber employed in the blend of the current invention is an amorphous, random, elastomeric copolymer of at least two monoolefins and a copolymerizable polyene. A preferred number of monoolefins is two but three or more may also be used. Usually one of the monoolefins is ethylene and the other is propylene. Other α-monoolefins may be used including those of the formula CH=CHR where R is an alkyl radical having up to 12 carbon atoms, such as butene-1, pentene-1, hexene-1, 4-methylpentene- 1 , 5-methylhexene-l, 4-ethylhexene- 1 , and the like.

It is preferred to include in the copolymer a small amount of at least one copolymerizable polyene to confer unsaturation on the copolymer. In practice it is usual to employ for this purpose a nonconjugated diene, including the open-chain non-conjugated diolefins such as 1 ,4-hexadiene or a cyclic diene. Preferred dienes include such bridged ring cyclic dienes as dicyclopentadiene or an alkylidenenorbornene as methylenenorbornene or ethylidenenorbornene as well as cyclooctadiene, methyltetrahydroindene and the like. The polymers employed are not limited to those having only two double bonds but may have three or more double bonds.

The polyolefin resin with which the monoolefin copolymer rubber is mixed to make the blend of this invention is a solid, high molecular weight resinous plastic material made by polymerizing such olefins as ethylene, propylene, butene-1, pentene-1, 4-methyl-pentene and the like in a conventional manner. Such crystalline polyolefins as polyethylene (of either the low- or high-density type) may be used, whether prepared by low- or high-pressure processes, including linear polyethylene. Polypropylene is a preferred polyolefin resin, having highly crystalline isotactic and syndiotactic forms. The density of polypropylene may range from 0.800 to 0.980 g/cc. Isotactic polypropylene with a density from about 0.900 to 0.910 g/cc may be particularly preferred. Crystalline block copolymers of ethylene and propylene, which are distinguished from amorphous, random ethylene-propylene elastomers, may also be used. Included among the polyolefin resins are the higher α-olefin modified polyethylenes and polypropylenes. As has been indicated, an important feature of this invention resides in partially curing the monoolefin copolymer rubber that is blended with polyolefin resin. For this purpose, it is preferred to use such free radical generating agents or crosslinking agents as the peroxides, whether aromatic or aliphatic, as have been mentioned above. This peroxide curative is used in conjunction with N,N'-m- phenylenedimaleimide. It is the combination of these materials which has been suφrisingly discovered to result in the desirable properties of low compression set and high tensile strength in the thermoplastic elastomeric blend.

The relative proportions of monoolefin copolymer rubber and polyolefin resin may vary widely. When expressed as percent of the total composition by weight, the level of monoolefin copolymer rubber may vary from about 10% to about 80% and the level of polyolefin resin may vary from about 10% to about 70%. More preferably, the level of monoolefin copolymer rubber may vary from about 20% to about 70%, and the preferable range for the level of polyolefin resin is from about 20% to about 60%. The levels of peroxide curative and N,N'-m-phenylenedimaleimide coagent may vary, as percent of the total composition, from about 0.1% to about 1.8%. A more preferred range of level of peroxide curative and coagent varies from about 0.3% to 1.0%. Most preferred 0.4 to 0.8%. The weight ratio of peroxide to N,N'-m- phenylenedimaleimide may vary from about 1 : 10 to about 10:1. A preferred ratio is from about 1 :4 to about 4: 1 . Most preferred is from 2: 1 to 1 :2. Any suitable other desired ingredients may be present in the elastomeric blend, such as particulate or fibrous fillers such as calcium carbonate, carbon black, silica, glass, clay, talc and the like. Other such materials may include extender or process oils such as paraffinic oils or naphthalenic oils, pigments, processing aids or lubricants, mold release agents, UV screening agents, antioxidants or stabilizers. Any conventional antioxidant or stabilizer may be used including amine types, phenolic types, and any other type desired.

Some examples of materials commonly used include 2,2,4-trimethy 1-1,2- dihydroquinoline, diphenylamine acetone condensate, aldol-α-naphthylamine, octylated diphenylamine, N-phenyl-N'-cyclohexyl-p-phenylenediamine, 2,6-di-t- butyl-4-methylphenol, styrene-resorcinol resin, o-cresolmonosulfide, di-p-cresol-2- propane, 2,5-di-t-amylhydroquinone, dilauryl-3,3'-thiodipropionate and the like.

Usually, the following or a similar procedure is used to carry out the invention: Step One: The monoolefin copolymer rubber, the polyolefin resin, the curing agent and coagent, and other optional additives, such as filler and oil, are charged at the desired ratio in a suitable mixer. Typically such mixers may be selected from the group consisting of a Banbury internal mixer, a transfer type extruder-mixer, a compounding extruder, or similar device that will enable efficient mastication at the desired temperature. Such blending apparatus may be preheated to reduce the time required to reach a processing temperature range, provided that such preheating temperature is below the decomposition temperature of the curing agent used.

Step Two: While mixing, the temperature is increased to above the decomposition temperature of the curing agent and usually the mix is held at such a temperature while continuing the mixing for a time period long enough to ensure at least 95% decomposition of the curing agent based on its theoretical half-life at that temperature and thorough mixing of the blend.

Step Three: After having processed the blend to a degree described in step two, an antioxidant is added to the blend and processing is continued usually for one minute or more in order to thoroughly incorporate the antioxidant into the blend for the puφose of deactivating any residual curing agent and enhance protection against oxidative degradation of the composition.

Step Four: If desired, the product of Step 3 may be refined on a mill before being used to form shaped articles by means of extrusion, injection molding, press molding, or other suitable means of manufacture.

Processability, as well as reprocessability, is an important characteristic of the blends of this invention. The processability of the blends may be evaluated by subjecting samples of the blend to such shaping operations as extrusion, injection molding, or compression molding. Extrusion is the shaping method of choice where long continuous forms, such as hose, window seals, wire coatings, flat sheets, and the like are desired. For satisfactory screw injection molding, the material must form a homogeneous article of uniform strength in the mold. The flow viscosity characteristics of such blends are adequate to insure filling the mold under the operating conditions. The most highly semicured blends of this invention are usually best shaped by press molding.

Up to now, certain desirable characteristics such as low compression set and good tensile properties at elevated temperature have largely been obtainable only in vulcanized elastomers which do not possess the qualities of being thermoplastic and reprocessable. Such low compression set results in good recoverability from deformation of the material and a resilient feel to articles made therefrom which approach the characteristics of vulcanized elastomers.

The partially cured blends of the present invention combine in one material the advantages of rapid moldability, reprocessability, and unexpectedly excellent performance with respect to compression set and tensile properties. Standard physical test methods were used to document the material performance advantages which are realized by the instant invention. Compression set at 158°F was measured by ASTM method D-395, and tensile properties by ASTM method D-412. Test pieces were normally cut out of flat slabs which had been injection molded from blends prepared according to the teachings of this invention. Definition of partially cured thermoplastic rubber

The extent of cure of the rubber in the finished compositions was determined by finding the percent of total rubber that is nonextractable in cyclohexane at room temperature(73F) in 48 hours. This number was calculated by measuring the insoluble or nonextractable fraction of the total compound and correcting for the soluble oils and insoluble polypropylene. In this invention, the term "partially cured" means that the percent of total rubber that is nonextractable or insoluable must be 93 percent or less.

The following examples are meant to illustrate the invention and are not intended to limit the scope of this invention in any manner whatsoever,

EXAMPLES

Example 1 and Comparative Examples A-D: Effect on Physical Properties of Rubber Compositions using N,N'-m-Phenylenedimaleimide and Other Coagents

Several blends were compounded in a Banbury internal mixer, following the general procedure described above. The monoolefin copolymer rubber employed in each blend (EPDM-1) contained 66% ethylene, 29% propylene, 5% ethylidenenorbornene by weight, and 75 phr of paraffmic extender oil. The Mooney viscosity of the rubber, ML 1+4 at 100°C was 67. The polyolefin resin used was a crystalline polypropylene homopolymer with a melt flow index of 4.0 as measured by ASTM D123-58T at 230°C and 2160 g load. The paraffmic oil used in all blends was Sunpar 150 from Sun Oil Co. The oil was used to bring the hardness of the blends into a range suitable for practical applications.

All of the compositions were dynamically partially cured with the organic peroxide 2,5-dimethyl-2,5-di(t-butyl-peroxy) hexane while undergoing mixing in the Banbury mixer at approximately 190°C. The finished blends were mechanically ground at room temperature, then injection molded into 76 x 152 x 3 mm slabs at

200 °C. The test data that appear in Table I were obtained from pieces cut from these slabs.

The test data in Table I clearly reveal the unique advantage obtained by using a combination of organic peroxide and N,N'-m-phenylenedimaleimide (Example 1) Compression set, as measured at 70 °C, 22 hours, by ASTM D-395, is significantly lower than is obtained by the use of the other coagents (Comparative Examples B, C, D) or by peroxide alone (Comparative Example A). Tensile strength, as measured at room temperature by ASTM D-412, is higher in Example 1 than in any of the other blends.

Table I

NOTES:

EPDM- 1 : Rubber consisting of ethylene 66%, propylene 29%, ethylidenenorbornene

5%, and 75 phr of paraffmic oil. Peroxide- 1 : 2,5,-dimethyl-2,5-di (t-butyl-peroxy)hexane, 50% active. Polypropylene: crystalline polypropylene homopolymer with a melt flow index of 4.0

(Profax 6501(4MFI)) Examples 2-4 and Comparative Examples E-G: Thermoplastic Elastomer Blends Using Peroxide Curative Alone and Peroxide Curative with N.N'-m- phenylenedimaleimide Three different monoolefin copolymer rubber grades were blended with polypropylene and other additives by the same procedure as in the preceding set of Examples and Comparative Examples. The rubber grades had varying proportions of ethylene, propylene, and ethylidenenorbornene as detailed in Table II.

Two sets of parallel blends were tested with each rubber: one set was prepared using peroxide curative alone (Comparative Examples E, F and G) and the corresponding set (Examples 2, 3, and 4) used the peroxide curative along with N,N'- m-phenylenedimaleimide.

In each corresponding set of blends, the use of peroxide curative together with N.N'-m-phenylenedimaleimide gave lower compression set and higher tensile strength than did the use of peroxide curative alone.

In all six compositions of Table II, the percent of nonextractable rubber was less than 93%. This verifies that improved compression set can be obtained in blends with composition of this invention while still having the rubber in a partially cured state.

When comparing the two sets of data in Table II, is may be concluded that the percent of non-extractable rubber is increased by using peroxide and N.N'-m- phenylenedimaleimide together, as opposed to using peroxide alone. The reported improvements in compression set and tensile strength may be attributable to the increased state of cure, or crosslinking, of the rubber.

Table II

NOTES:

EPDM-2: Rubber consisting of ethylene 52%, propylene 40%, ethylidenenorbornene 8%. Mooney viscosity ML 1+4 at 100 deg C 82.

EPDM-3 : Rubber consisting of ethylene 64%, propylene 28%), ethylidenenorbornene 8%. Mooney viscosity ML 1+4 at 100 deg C 80.

EPDM-4: Rubber consisting of ethylene 52%, propylene 39%, ethylidenenorbornene 9%. Mooney viscosity ML 1 +4 at 100 deg C 99.

Polybutene Oil: Indopol H-300 plasticizer from Amoco Chemical Co. Other ingredients are the same as in Table I.

Examples 5. 6 and Comparative Examples H-O: Evaluation of the Effect of Several Coagents with Peroxide Cure

It was desired to evaluate the effect of several coagents in peroxide cured thermoplastic vulcanizates. The other coagents tested included a crosslinking monomer coagent of trimethylolpropane trimethacrylate; triallyl cyanurate 75%).; and 1 ,2-polybutadiene. The peroxy curative was 2,5-dimethyl-2,5-di(t-butyl-peroxy) hexane (50%> active material).

Comparative Example H is the only one with no curative; Comparative Example I is cured with only peroxide and no coagent. The other formulations used the peroxy compound and two different amounts of coagent, as can be seen in the Table.

In the Examples and Comparative Examples of Table III, it can be observed that the coagent N,N'-m-phenylenedimaleimide gave lower compression set and higher tensile strength in comparison to the other formulations. The examples and comparative examples shown in Table III were used in the same manner as those in Tables I and II.

Table III

NOTES:

EPDM-5 is a 70/30 Ethylene/propylene rubber containing 43% paraffmic oil, having a Mooney viscosity ML 1+4 at 100 deg C =60. The above compositions therefore contain 56% total oil, and 40% rubber hydrocarbon. Antixoidant: Tetrakis(methylene 3-(3,5-di-t butyl-4-hydroxyphenyl)-propionate) methane

Claims

We Claim:

1. A process of making a thermoplastic elastomeric filled composition comprising:

(a) about 25-85 parts by weight of crystalline thermoplastic polyolefin resin;

(b) about 75-15 parts by weight of monoolefin copolymer rubber per 100 parts total of (a) plus (b), wherein said monoolefin copolymer rubber is a polymer of monomers comprising ethylene or propylene, and at least one other alpha olefin of the formula CH₂=CH_R in which R is alkyl of 1 to 12 carbon atoms and from none to a minor portion of at least one non-conjugated diene;

(c) about 0.1 to about 1.8 percent by weight of (a) plus (b) of a peroxide curative;

(d) about 0.1 to about 1.8 percent by weight of (a) plus (b) of an N.N'-m- phenylenedimaleimide coagent; (e) 0 to 300 percent by weight of (a) plus (b) filler; and

(f) 0 to 200 percent by weight of (a) plus (b) oil; said process comprising: blending (a), (b), (c) and (d) at a temperature sufficient to melt said resin; then masticating the blend continuously at a temperature at least as high as the decomposition temperature of the peroxide for a time sufficient to decompose 95 percent of the peroxide to form a composition in which the percent of total rubber that is non-extractable in cyclohexane at room temperature in 48 hours is less than or equal to 93 percent.

2. The process of claim 1 wherein the polyolefin resin is polypropylene, present at about 25-75 parts by weight and the rubber is EPDM rubber, present about

75-25 parts by weight, said EPDM rubber being a product of the polymerization of ethylene, propylene and a lesser quantity of a non-conjugated diene.

3. The process as recited in claim 1 wherein the individual amounts of each of peroxide curative and coagent is present in the range of from about 0.3%) to 1.0%.

4. The process as recited in claim 1 wherein the weight ratio of peroxide - to N,N'-m-phenylenedimaleimide varies from about 1 : 10 to about 10:1.

5. The process as recited in claim 1 wherein the weight ratio of peroxide to N.N'-m-phenylenedimaleimide varies from about 1 :4 to about 4:1.

6. The process of claim 1 wherein the peroxide curative is selected from the group consisting of aromatic diacyl peroxides and aliphatic diacyl peroxides, dibasic acid peroxides, ketone peroxides, alkyl peroxyesters, alkyl hydroperoxides, including diacetylperoxide, dibenzoyl peroxide, bis-2,4-dichloro benzoyl peroxide, di- t-butyl peroxide, dicumylperoxide, t-butylperbenzoate, t-butylcumyl peroxide, 2,5-bis (t-butylperoxy)-2,5-dimethylhexane, 2,5-bis (t-butylperoxy)-2,5-dimethylhexyne-3, 4,4,4',4'-tetra(t-butylperoxy)-2,2-dicyclohexylpropane, 1 ,4-bis-(t-butyl)-peroxy- isopropylbenzene, l,l-bis-(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl- 2,5-di(t-butyl-peroxy) hexane, lauroyl peroxide, succinic acid peroxide, cyclohexanone peroxide, t-butyl peracetate, butyl hydroperoxide.

7. The process according to claim 1 further comprising the step of blending an antioxidant into the composition after a time sufficient to decompose 95 percent of the peroxide; and further mixing for a time suffcient to disperse said antioxidant in the blend and completely inactivate any residual peroxide.

8. The process according to Claim 2 in which theEPDM rubber has a Mooney viscosity, ML 1+4 at 100┬░C, between 10 and 120.

9. The process according to Claim 2 in which the non-conjugated diene content of the EPDM rubber is in the range of 2 to 10% by weight.

10. The process of Claim 2 in which the EPDM rubber contains 20 to 100 phr of extender oil.

11. The process of Claim 1 in which the nonconjugated diene is ethylidene norbornene.

12. The process as recited in claim 1 wherein the individual amounts of each of peroxide curative and coagent is present in the range of from about 0.1 % to 1.8%.