Abstract: Modified rubber compositions comprise by weight about 15-60% of a highly saturated aliphatic rubber such as ethylene-propylene-diene rubber, about 25-80% of acrylate monomer units; and less than about 5% multi-functional monomer units. The compositions exist as amorphous heterogeneously dispersed phases. The first phase comprises the copolymer rubber to which polymers of at least 10% of the other monomer units are grafted. The second phase comprises the other monomers polymerized as homo and copolymers, not grafted to the rubber. Optionally, up to 20% of the composition comprises high index monomer units. The high index monomer units may be copolymerized with the acrylate and grafted to the rubber. Greater than 10% of the monomer units other than rubber are grafted to the rubber. The number average molecular weight of the grafts is between 10,000 and 80,000 daltons.