Polyacrylate elastomer compositions

Abstract

A vulcanizable polyacrylate elastomer composition having improved resistance to hydrocarbon oils is provided which comprises one or more lower alkyl acrylic acid ester monomers polymerized with a comonomer containing either a halogen or an epoxy group, in the presence of from about 0.25 to 10 percent, by weight of total monomer, of a low molecular weight, unsaturated polymer of butadiene or isoprene or copolymers thereof with styrene or acrylonitrile. In addition, a process for preparing such elastomer compositions is also provided, together with the vulcanization of such elastomers and the resulting vulcanized polyacrylate.

Description

Generally stated the subject matter or the present invention relates to improved polyacrylate elastomer compositions. More particularly, the invention relates to vulcanizable polyacrylate elastomer compositions which have improved resistance to degradation by hydrocarbon oils, and to a process for preparing such compositions.

BACKGROUND OF THE INVENTION

Polyacrylate elastomers are well known specialty elastomers having extensive utility in the automative industry as gasketing material, oil seals, O-rings, transmissions seals, and the like. In effect such elastomers are employed where resistance to hot oil is important and in such usage the retention of physical properties is of paramount importance.

There are available a number of polyacrylate elastomers finding use in the automotive industry and other industries. Note U.S. Pat. No. 3,201,373, Kaizerman, which discloses polyacrylate elastomers derived from copolymerization of a major proportion of a lower alkyl acrylate with vinyl chloroacetate. Similarly, P. Fram in the Encyclopedia of Polymer Science and Technology 1, 226 (1964) describes polyacrylates wherein other halogen containing comonomers, such as vinyl chloroethyl ether, are copolymerized with alkyl acrylates. Polyacrylates are described which are composed of, in addition to alkyl acrylates, alkoxy-alkyl acrylates, cyanoalkyl acrylates and alkylthioalkylacrylates. Note U.S. Pat. No. 3,450,681, Gobran et al, and U.S. Pat. No. 3,488,331, Joregenson. The status of vulcanizable polyacrylate elastomers up to the present time is reviewed by T. M. Vial in Rubber Chemistry and Technology, "Rubber Reviews", April, 1977. These elastomers are vulcanizable by a variety of means which is also summarized in the article.

The property of acrylate elastomers which is probably most important in their application is oil resistance, a term encompassing several properties, including volume swell and retention of physical properties after exposure to hot oil for a period of time. This exposure usually involves softening, loss of modulus and gain in elongation due to plasticizing or the swelling action of the oil, as well as thermal degradation.

However, in spite of the generally favorable oil resistance of polyacrylate elastomers there is always a search for means whereby oil resistance can be improved to obtain longer life in service. Anything which provides better retention of properties on exposure to hot oil, other things being equal, is desirable. The present invention represents the culmination of a series of investigations conducted largely by the inventors and their associates directed to improving the oil resistance of polyacrylate elastomers.

Accordingly, it is a primary object of the present invention to provide vulcanizable polyacrylate elastomer compositions having improved resistance to hydrocarbon oils.

Another object of the present invention is to provide a method for improving the oil resistance of vulcanizable polyacrylate elastomer compositions.

It is a further object of the present invention to provide a vulcanized elastomer having improved resistance to hydrocarbon oils.

Generally then, it is an object of this invention to provide an improved vulcanized elastomer which retains its physical properties when employed in a hot oil environment. This retention results in a significant lengthening of the service life of materials prepared from such elastomers.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be realized by practice of the invention, the objects and advantages being realized and attained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.

THE INVENTION

To achieve the forgoing objects, and in accordance with its purpose, as embodied and broadly described in the present invention relates to vulcanizable polyacrylate elastomer compositions having improved resistance to hydrocarbon oils which comprises a polymer of at least one acrylic acid ester monomer co-polymerized with a monomer containing a halogen or an epoxy group, in the presence of from about 0.25 to 10 percent, by weight of total monomer, of a low molecular weight, unsaturated polymer of butadiene or isoprene or copolymers thereof with styrene or acrylonitrile.

The present invention further provides a method for preparing a vulcanizable polyacrylate elastomer having improved resistance to hydrocarbon oils.

In addition, the invention also provides a vulcanized elastomer having improved resistance to hydrocarbon oils.

The invention consists of the novel methods, processes, steps and improvements herein shown and described. In addition, it should also be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

In essence, the present invention resides in the discovery that the polymerization of an acrylic acid ester and a comonomer containing either a halogen or epoxy group, in the presence of an unsaturated, low molecular weight polymer will result in vulcanizable polyacrylate elastomers having an improved resistance to hydrocarbon oils. This result is clearly surprising and wholly unexpected, since the art is devoid of any teaching which discloses or suggests this improvement in oil resistance. In fact it would be reasonable to conclude that the opposite effect would result, since such low molecular weight polymeric hydrocarbons are notorious for having little to no oil resistance.

The polymers are viscous liquids having a molecular weight of from about 500 to 4000. They are hydroxyl or aromatic hydrocarbon terminated homopolymers of butadiene or isoprene or copolymers thereof with minor amounts of styrene or acrylonitrile. Based on the monomeric butadiene or isoprene in the polymer, the unsaturation is about 75% to 99%; most of the unsaturation is vinyl and trans-1,4, with small amounts of the unsaturation internally cyclized. Examples of such polymer are described in Product Bulletin No. 154-570 and No. 155-570, Lithinum Corp. of America, and Research Bulletin No. 508, Poly R-D, Sinclair Petrochemicals, Oct. 1, 1968.

The acrylic acid ester component of the composition comprises one or more lower alkyl acrylates, that is, esters of acrylic acid and alcohols containing from about 1 to 8 carbon atoms, such as methyl, ethyl, n-butyl, n-hexyl, 2-ethylhexyl and n-octylacrylates, and the like. Also suitable are the alkoxyethyl and alkylthioethyl acrylates having the structural formula: ##STR1## wherein R is lower alkyl containing from 1 to 8 carbon atoms, particularly methyl or ethyl, and X is oxygen or sulfur. Other useful monomers include cyanoalkyl acrylates and cyanoalkoxyalkyl acrylates having the formulae: ##STR2## wherein R is a straight or branced chain alkylene radical containing from 2 to 8 carbon atoms and X is oxygen or sulfur.

The halogen or epoxy containing comonomers useful in providing the vulcanization sites in the polyacrylates include, for example, 2-chloroethyl vinyl ether, vinyl chloroacetate, 2-chloroethyl acrylate; compounds having the formulas: ##STR3## allyl glycidyl ether, glycidyl methacrylate, and the like.

Normally the halogen or epoxy containing monomer represents a minor proportion of the total monomer mixture, for example, up to about 10% by weight. The remainder of the monomer mixture contains either a single ester of acrylic acid, for example, ethyl acrylate, a mixture of acrylic esters, such as ethyl and butyl acrylate, or a mixture of one or more alkyl acrylates and an alkoxyethyl acrylate, alkylthioethylacrylate or a cyanoalkylacrylate or cyanoalkoxyalkyl acrylate. The preferred compositions for the purposes of this invention contain either ethyl acrylate copolymerized with vinyl chloroacetate, a mixture of ethyl and butyl acrylate copolymerized with vinyl chloroacetate, mixtures of ethyl acrylate, butyl acrylate and methoxy - or ethoxy-ethyl acrylate with vinyl chloroacetate, or mixtures of ethyl acrylate, butyl acrylate and cyanoethyl acrylate with vinyl chloroacetate. Optionally, in addition to the esters of acrylic acid described and the halogen or epoxy monomer, there can be used minor amounts of other co-polymerizable monomers, e.g. acrylonitrile.

The present invention may also be generally described as a conventional emulsion or suspension polymerization of one or more esters of acrylic acid, with a comonomer containing a halogen or epoxy group in the presence of a low molecular weight, unsaturated hydrocarbon polymer.

The copolymerization, whether by emulsion or suspension techniques, is conducted using a conventional free radical catalyst, such as benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, or a redox system, in the presence of a small amount, from about 0.25 to 10 percent of an unsaturated low molecular hydrocarbon weight polymer.

While a butadiene or isoprene polymer may be incorporated into the polyacrylate by blending, for example on a rubber mill, it is not as effective in providing improved oil resistance, although some improvement is obtained.

The polyacrylate elastomers containing the low molecular weight unsaturated hydrocarbon polymer are compounded in conventional manner with carbon black or other fillers, vulcanizing agents, accelerators, antioxidants, and the like, and vulcanized. Best results are obtained if the compositions are vulcanized in accordance with the procedures set forth in U.S. Pat. No. 3,458,461, Mihal and U.S. Pat. No. 3,506,624, Behrens. However, the polymers may be cured using other systems known to those skilled in the art, such as by the use of ammonium salts, and the like.

The following examples are provided for illustrative purposes and they may include particular features of the invention. However, the examples should not be construed as limiting the invention, many variations of which are possible without departing from the spirit or scope thereof.

EXAMPLE I

Preparation of Polymer

To a stirred suspension system comprising 150 parts water, 6.5 parts tricalcium phosphate and 3.5 parts Bentonite clay was added a solution comprising 71.75 parts ethyl acrylate, 15.6 parts vinyl chloroacetate, 0.04 parts dodecyl mercaptan and 0.1 part azobisisobutyronitrile. A solution comprising 256.5 parts ethyl acrylate, 5.25 parts vinyl chloroacetate, 0.056 part dodecyl mercaptan and 3.75 parts ARCO R-15M Resin (a low molecular weight polybutadiene) dissolved in 3 parts ethyl acrylate was added to the above mixture over a period of one hour. The polymerization reaction was maintained at about 80.degree. C., and the mixture was stirred for an additional 30 minutes after all monomers were added. The reaction mixture was then steam distilled to remove unreacted monomers and the polymer was filtered, washed and dried.

EXAMPLE II

This example demonstrates the effectiveness of the use of a small amount of polybutadiene to improve te high temperature oil aging properties of an acrylic elastomer.

______________________________________ Parts by Weight A B______________________________________Polymer A.sup.1 100 --Polymer B.sup.2 -- 100Carbon black (FEF) 60 60PBNA.sup.3 2 2Stearic acid 1 1Sulfur 0.2 0.2HVA No. 2.sup.4 0.75 0.75Sodium Caprylate 4 4______________________________________ .sup.1 94% ethyl acrylate - 6% vinyl chloroacetate .sup.2 Same as Polymer A, but prepared in presence of 1% by weight polybutadiene (ARCO R-15M Resin-Sinclair Petrochemicals, Inc.) .sup.3 Phenyl-beta naphthylamine .sup.4 m-phenylenebismaleimide

The above compositions were mixed in conventional manner on a two-roll mill, as set forth in U.S. Pat. No. 3,506,624, Behrens, for 10 minutes at 330.degree. F. and post-cured for 4 hours at 176.degree. C. Physical properties are shown in Table 1.

TABLE 1______________________________________ A B______________________________________Modulus at 100%, psi 1400 1500Tensile, psi 1865 1735Elongation at break, % 150 120Shore A hardness 79 79______________________________________

The compositions were then aged for 2 weeks at 176.degree. C. in ASTM No. 3 oil and retested. Oil aging is conducted in accordance with ASTM D471 at 176.degree. C. Resistance to oil is manifested by retention of physical properties after aging. Data are shown in Table 2.

TABLE 2______________________________________ A B______________________________________Modulus at 100%, psi 760 1420Tensile, psi 1660 2150Elongation at break, % 230 140Shore A hardness 62 64______________________________________

These data demonstrate the improvement, retention of original properties, of Composition B versus Composition A.

EXAMPLE III

______________________________________ Parts by Weight______________________________________Polymer.sup.1 100Carbon black (FEF) 60PBNA 2Stearic Acid 1Sulfur 0.25Sodium oleate 4______________________________________ .sup.1 94% ethyl acrylate - 6% vinyl chloroacetate prepared in presence o 10% by weight of polybutadiene (ARCO R-15M Resin-Sinclair Petrochemicals, Inc.)

The above formulation was compounded on a standard rubber mill and cured at 330.degree. F. for 10 minutes; post-cured 4 hours at 176.degree. C. Properties are shown in Table 3.

TABLE 3______________________________________Modulus at 100%, psi 1040Tensile, psi 1955Elongation at break, % 160Shore A hardness 65______________________________________

After aging the above compositions for 2 weeks at 176.degree. C. in ASTM No. 3 oil, they exhibited the properties shown in Table 4.

TABLE 4______________________________________Modulus at 100%, psi 900Tensile, psi 1340Elongation at break, % 130Shore A hardness 57______________________________________

Retention of properties after aging is shown to be improved to nearly the same degree as polybutadiene used at a level of 1%.

EXAMPLE IV

______________________________________ Parts by Weight A B C D______________________________________Polymer A.sup.1 100 100 -- --Polymer B.sup.2 -- -- 100 100 Parts by Weight A B C D______________________________________Carbon black (FEF) 60 60 60 60Antioxidant.sup.3 2 2 2 2Stearic Acid 1 1 1 1Sulfur 0.2 0.2 0.2 0.2Sodium caprylate 4 4 4 4______________________________________ .sup.1 94%-(82% ethyl acrylate - 18% butyl acrylate) -6% vinyl chloroacetate; Composition B prepared in presence of 1% by weight polybutadiene (ARCO R15M Resin-Sinclair Petrochemicals, Inc.) .sup.2 94%-(50% ethyl acrylate - 50% methoxyethylacrylate) -6% vinyl chloroacetate. Composition D prepared in presence of 1% polybutadiene (ARCO %-15M Resin-Sinclair Petrochemicals, Inc.) .sup.3 Di-beta-naphthyl-p-phenylene diamine

The compositions were compounded on a standard rubber mill and cured for 15 minutes at 330.degree. F.; post-cured for 4 hours at 176.degree. C. They exhibited the properties shown in Table 5.

TABLE 5______________________________________ A B C D______________________________________Modulus at 100%, psi 975 1000 995 1410Tensile, psi 1735 1980 1840 2000Elongation at break, % 160 160 170 135Shore A hardness 75 68 68 72______________________________________

Following oil aging for 2 weeks at 176.degree. C. in ASTM No. 3 oil they showed the properties in Table 6.

TABLE 6______________________________________ A B C D______________________________________Modulus at 100%, psi 300 460 450 760Tensile, psi 1210 1550 1425 1725Elongation at break,% 385 230 235 180Shore A hardness 44 44 48 61______________________________________

Compositions B and D show greater retention of properties after aging in hot oil than A and C, respectively, which are of similar composition without the improvement of this invention.

EXAMPLE V

______________________________________Formulation (parts by weight) A B C______________________________________Polymer.sup.1 100 100 100Carbon black (FEF) 60 60 60Stearic acid 1 1 1sulfur 0.25 0.25 0.25Sodium caprylate 4 4 4______________________________________ .sup.1 94% - ethyl acrylate - 6% vinyl chloroacetate; composition B prepared in presence of 1% by weight of Lithene AM and composition C in the presence of 1% by weight of Lithene PM (both polybutadienes - Lithium Corp. of America) The above formulations were compounded on a standard rubber mill and cured for 10 minutes at 330.degree. F; post-cured for 4 hours at 176.degree. C. They exhibited the properties shown in Table 7.

The above formulations were compounded on a standard rubber mill and cured for 10 minutes at 330.degree. F.; post-cured for 4 hours at 176.degree. C. They exhibited the properties shown in Table 7.

TABLE 7______________________________________ A B C______________________________________Modulus at 100%, psi 1750 1850 1775Tensile, psi 1985 2050 1825Elongation at break, 1% 110 100 100Shore A hardness 73 75 81______________________________________

Following aging at 176.degree. C. for 2 weeks in ASTM No. 3 oil the compositions exhibited the properties shown in Table 8.

TABLE 8______________________________________ A B C______________________________________Modulus at 100%, psi 375 750 875Tensile, psi 1475 1875 1700Elongation at break, % 340 190 165Shore A hardness 53 58 61______________________________________

Compositions B and C show greater retention of properties than Composition A.

EXAMPLE VI

______________________________________ Parts by Weight A B C D______________________________________Elastomer A.sup.1 100 100 -- --Elastomer B.sup.2 -- -- 100 100Carbon black 60 60 60 60Stearic acid 1 1 1 1Sulfur 0.25 0.25 0.25 0.25Sodium Caprylate 4 4 4 4Antioxidant.sup.3 2 2 2 2______________________________________ .sup.1 94% - (50% ethyl acrylate - 25% butyl acrylate - 25% methoxymethyl acrylate) - 6% vinyl chloroacetate; composition B prepared in presence of 1% by weight of ARCO R-15 M Resin. .sup.2 97% - (50% ethyl acrylate - 25% butyl acrylate - 25% ethoxyethyl acryate) - 3% vinyl chloroacetate; composition D prepared in presence of 1% by weight ARCO R-15M Resin. .sup.3 Di-beta naphthyl-p-phenylene diamine.

The compositions were mixed on a standard rubber mill and cured for 15 minutes at 330.degree. F. Post-cured for 4 hours at 176.degree. C. They exhibited the properties shown in Table 9.

TABLE 9______________________________________ A B C D______________________________________Modulus at 100%, psi 1255 1340 800 850Tensile, psi 1875 1945 1640 1735Elongation at break, % 130 140 190 180Shore A hardness 70 71 68 70______________________________________

Following aging for 2 weeks at 176.degree. C. in ASTM No. 3 oil they exhibited the properties shown in Table 10.

TABLE 10______________________________________ A B C D______________________________________Modulus at 100%, psi 460 705 350 590Tensile, psi 1380 1625 1200 1330Elongation at break, % 260 190 310 180Shore A hardness 48 53 45 50______________________________________

Compositions B and D show greater retention of original properties following oil aging than either of compositions A and C.

Claims

1. A vulcanizable polyacrylate elastomer composition having improved resistance to hydrocarbon oils which comprises one or more lower alkyl acrylic acid ester monomers copolymerized with a monomer selected from the group consisting of .beta.-chloroethyl vinyl ether, vinyl chloroacetate, .beta.-chloroethyl acrylate, allyl glycidyl ether, glycidyl methacrylate and compounds having the formulae ##STR4## in the presence of from about 0.25 to 10 percent, by weight, of total monomer, of a liquid unsaturated, hydroxyl or aromatic hydrocarbon terminated homopolymer of butadiene or isoprene, or copolymers thereof with minor amounts of styrene or acrylonitrile, having a monomeric weight of from about 500 to 4,000 and containing from about 75% to 99% unsaturation, based on the monomeric butadiene or isoprene in the polymer.

2. A composition according to claim 1 wherein the low molecular weight polymer is polybutadiene.

3. a composition according to claim 1 wherein the low molecular weight polymer is polyisoprene.

4. A composition according to claim 1 wherein the low molecular weight polymer comprises a major proportion of butadiene and a minor proportion of acrylonitrile or styrene.

5. A composition according to claim 1 wherein the acrylic acid ester monomer is a lower alkyl acrylate containing from 1 to 8 carbon atoms in the alkyl group.

6. A composition according to claim 1 which comprises in addition to at least one or more lower alkyl acrylic acid esters a monomer which is an alkoxyethyl acrylate or an alkylthioethyl acrylate having the general formula: ##STR5## wherein R is lower alkyl and X is oxygen or sulfur.

7. A composition according to claim 1 which comprises in addition to at least one or more lower alkyl acrylic acid esters a monomer which is a cyanoalkyl acrylate or a cyanoalkoxyalkyl acrylate having the general formulae: ##STR6## wherein R is a straight or branched chain alkylene radical containing from 2 to 8 carbon atoms and X is oxygen or sulfur.

8. A composition according to claim 1 wherein the halogen or epoxy containing comonomer comprises a minor proprotion of the total monomer mixture.

9. A composition according to claim 1 wherein the halogen or epoxy containing comonomer comprises up to about 10 percent by weight of the total monomer mixture.

10. A composition according to claim 1 wherein the total monomer comprises ethyl acrylate with vinyl chloroacetate, a mixture of ethyl and butyl acrylate with vinyl chloroacetate or mixtures of ethyl acrylate, butyl acrylate and methoxy or ethoxy-ethyl acrylate with vinyl chloroacetate.

11. A method for preparing the vulcanizable polyacrylate elastomer of claim 1 which comprises polymerizing an ester of an acrylic acid with a comonomer selected from the group consisting of .beta.-chloroethyl vinyl ether, vinyl chloroacetate, .beta.-chloroethyl acrylate, allyl glycidyl ether, glycidyl methacrylate and compounds having the formulae ##STR7## in the presence of a liquid unsaturated, hydroxyl or aromatic hydrocarbon terminated homopolymer of butadiene or isoprene, or copolymers thereof with minor amounts of styrene or acrylonitrile, having a monomeric weight of from about 500 to 4,000 and containing from about 75% to 99% unsaturation, based on the monomeric butadiene or isoprene in the polymer.

12. A method according to claim 11 wherein the polymerization technique is emulsion polymerization.

13. A method according to claim 11 wherein the polymerization technique is suspension polymerization.

14. A method according to claim 11 wherein polymerization is conducted in the presence of a conventional free radical cayalyst in an amount sufficient to catalyze polymerization.

15. A method according to claim 14 wherein the catalyst is benzoyl peroxide, dicumyl peroxide or azobisisobutyronitrile.

16. A method according to claim 11 wherein polymerization is conducted in the presence of a redox catalyst system in an amount sufficient to catalyze polymerization.

17. A method according to claim 11 wherein the resulting polymer is vulcanized.

18. A vulcanized polyacrylate elastomer having improved resistance to hydrocarbon oils prepared according to the process of claim 17.