Rubber composites suitable for tire sidewalls from hexadiene polymer

An elastomeric composition consisting essentially of, based on 100 parts by weight rubber (A) about 15 to about 60 parts by weight of rubbery polymer of at least one nonconjugated diolefin having the formula:

• ##STR4## where R.sub.1, R.sub.2 and R.sub.3 are hydrogen, a lower alkyl group containing up to 4 carbon atoms or an aryl group, and R.sub.4 is a lower alkyl group containing up to 4 carbon atoms or an aryl group, (B) about 85 to about 40 parts by weight of high unsaturation rubber selected from the group consisting of at least one of natural high cis-1,4-polyisoprene rubber, synthetic high cis-1,4-polyisoprene, high cis-1,4-polybutadiene, butadiene/styrene rubber and polyalkenylenes and (C) 0 to about 40 parts by weight of at least one low unsaturation rubber selected from an EPDM and halobutyl rubber, where said EPDM rubber is an ethylene-propylene-nonconjugated diene terpolymer containing from about 20 to about 75 weight percent units derived from ethylene, from about 80 to 25 weight percent units derived from propylene, and a minor proportion of from about 1 to 15 weight percent units derived from a C.sub.5 -C.sub.30 nonconjugated diene and where said halobutyl rubber is a chlorinated or brominated butyl rubber prepared by copolymerization of isobutylene and isoprene to form a butyl-type rubbery copolymer containing about 95 to about 98 weight percent isobutylene and, correspondingly, about 5 to about 2 weight percent isoprene and then chlorinating or brominating said copolymer to form the halobutyl rubber containing about 0.5 to about 2.0 weight percent chlorine or bromine and about 0.5 to about 3.5 mole percent unsaturation expressed in units of carbon-to-carbon double bonds per kilogram of polymer.