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 crosslinking 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
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