Elastomeric polymers and compounded elastomers having reduced amounts of leachables and improved resistance to -irradiation sterilization suitable for pharmaceutical stopper and seal applications. These polymers and compounded elastomers maintain their physical performances upon being exposed to -irradiation over time and typical use conditions. The polymer is prepared by reacting a mixture of i) a C.sub.4 to C.sub.7 isoolefin monomer, ii) a styrene based monomer, and optionally iii) a C.sub.4 to C.sub.14 multiolefin monomer wherein the polymer contains 5 to 15 wt % of styrene derived units.

Elastomeric polymers and compounded elastomers having reduced amounts of leachables and improved resistance to -irradiation sterilization suitable for pharmaceutical stopper and seal applications. These polymers and compounded elastomers maintain their physical performances upon being exposed to -irradiation over time and typical use conditions. The polymer is prepared by reacting a mixture of i) a C.sub.4 to C.sub.7 isoolefin monomer, ii) a styrene based monomer, and optionally iii) a C.sub.4 to C.sub.14 multiolefin monomer wherein the polymer contains 5 to 15 wt % of styrene derived units.

Polymeric compositions and processes of forming the same are discussed herein. The processes generally include contacting a polylactic acid with a reactive modifier selected from epoxy-functionalized polybutadiene, ionic monomer, and combinations thereof.