Vulcanizable tire innerliner compositions are described which are essentially free of halogen atoms or contain a reduced halogen content. The innerliners contain a saturated elastomeric interpolymer of a C.sub.4 -C.sub.7 isomonoolefin, e.g., isobutylene and a para-alkylstyrene e.g., para-methylstyrene, which contains benzylic ester functionality having 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.Innerliners of the invention provide excellent impermeability to air, heat aging properties and good adhesion to tire carcass stock required for tire innerliners, and are also essentially free of halogen or contain low halogen content thereby reducing environmental concerns occasioned by the incineration of used tires.