A. Field of the Invention
This invention relates to sulfur vulcanizable interpolymers of monomers comprising a major amount of one or more olefins and one or more saturated alkyl acrylates and a minor amount of one or more acyclic conjugated diolefins. More particularly, this invention relates to elastomeric terpolymers of said monomers prepared with a catalyst system comprising a Lewis acid, a vanadium compound and a source of free-radicals such as organic peroxides, ultraviolet light, high energy radiation and the like. Most particularly, this invention relates to sulfur vulcanizable terpolymers of said monomers in which the polymer backbone chain of carbon atoms consists of segments of alternating olefin and acrylate monomer units of variable length interconnected by randomly distributed conjugated diolefin monomer units; and the process for producing these particular terpolymers. Analysis of the interpolymers indicates that the mol percent of the acrylate esters and the sum of the mol percentages of the olefin and diolefin monomers present in the interpolymer are each substantially equal to 50 mol percent.
The interpolymers made by the catalyst system and process of this invention have in the uncured state an inherent viscosity in excess of 0.5 when measured in benzene or toluene at 25.degree. C. at a concentration of 0.1 g/dl, and a glass transition temperature below 0.degree. C. When the interpolymers of this invention are vulcanized with the aid of sulfur and accelerators the vulcanizates exhibit high tensile, elongation and modulus. They may be readily compounded with other elastomers or with fillers such as talc and reinforcing agents such as carbon blacks and extended with process oils, resins and plasticizers.
B. Prior Art
The preparation of alternating copolymers containing 50 mole percent of each monomer is old in the art as exemplified by the copolymers of styrene and maleic anhydride; and methyl vinyl ether-maleic anhydride, made with the aid of free-radical catalysts such as organic peroxides or azo compounds. Copolymers of olefins and diolefins such as isobutene, styrene and butadiene with polar monomers such as acrylonitrile, alkyl acrylates and methyl vinyl ketone cannot be prepared with cationic initiators and the free-radical initiated copolymerization of these systems of monomers is also ineffective since degradative chain transfer reactions lead to low incorporation of the olefin component in the copolymer and low molecular weight products.
Earlier work in these laboratories, described in U.S. Pat. Nos. 3,183,217, 3,278,503 and 3,426,005 showed that copolymers of high molecular weight having about 50 mole percent of each monomer could be prepared from olefinic, diolefinic and vinylic monomers such as isobutylene, 2-methyl-1-pentene, butadiene, styrene and vinyl ethers with polar monomers such as acrylonitrile, alkyl acrylates, acrolein and vinyl acetate if the polar monomer is first complexed with a Lewis acid such as zinc chloride or boron fluoride. It was also shown that the presence of organic peroxides or metal alkyl compounds enhanced the polymerization rate.
More recently, British Patent 1,187,105 based on Japanese Application 36,745, discloses the interpolymerization of olefins, polyenes and polar monomers using as a catalyst system (1) an organoaluminum (or boron) halide, MR.sub.n X.sub.3 -n; or a mixture of at least two compounds having the general formula (a) MR.sub.n X.sub.3 -n, (b) M'R'.sub.3 and (c) M"X.sub.3 or (2) an organometal halide complex prepared by contacting one of the disclosed monomers with (a) an organometallic compound of a metal of Groups IIb, IIIb, or IVb with (b) a halide of a metal of Groups IIIb or IVb, at least one of the latter (a) or (b) being a compound or aluminum or boron, and (3) an organic peroxide.
Canadian Patent 909,423 discloses blends of low unsaturated rubbers such as BUTYL rubber and EPDM with alternating copolymers of olefins and alkenyl acrylates, in which the alkenyl radical is unsaturated, either terminally or internally.
U.S. Pat. No. 3,637,611 discloses the preparation of alternating copolymers of an olefin or polyene with an .alpha.,.beta. or .alpha.,.beta. multisubstituted conjugated vinyl compound by first complexing the said vinyl compound with an organoaluminum or organoboron halide and then contacting the complex with the olefinic compound.
U.S. Pat. No. 3,752,788 discloses alternating multicomponent copolymers composed of at least one unsaturated ether compound as a Group (A.sub.1) monomer, at least one Group (A.sub.2) monomer, selected from olefins, internal olefins and polyenes; and at least one Group (B) monomer having a carbon to carbon double bond at a conjugated position to a carbonyl or nitrile group, said copolymer having a structure such that monomer units from Groups (A.sub.1) and (A.sub.2) always alternate with monomers from Group (B). The alternating copolymer is produced by contacting the monomers with an organoaluminum or organoboron halide.