Abstract: A compatibilized polymer blend composition is provided which comprises a mixture of an elastomeric polymer and an acid-grafted polymer of an isomonoolefin and an alkylstyrene such as a blend of EPDM and a maleic anhydride-grafted copolymer of isobutylene and para-methylstyrene.

Abstract: Intervulcanized compositions having improved curing efficiency are prepared by the free radical curing of a mixture of an ethylenically unsaturated diolefin polymer such as natural or synthetic rubber and a saturated or low unsaturation polymer such as an isobutylene/para-methylstyrene copolymer which contains functional groups pendant to the polymer chain. These functional groups contain an olefinic or vinyl double bond positioned alpha, beta to a substituent group which activates the double bond towards free radical addition reactions with the diolefin polymer. Preferred functionality includes benzylic ester functionality represented by the structure: ##STR1## wherein R.sub.2 and R.sub.3 are independently selected from hydrogen or C.sub.1 to C.sub.6 alkyl, and R.sub.4 is selected from hydrogen, C.sub.1 to C.sub.28 alkyl, aryl or C.sub.2 to C.sub.28 alkenyl.