Abstract: Disclosed herein is a copolymer comprising the polymerization product of propylene and a branched olefin, the copolymer comprising about 80 to about 99.9 wt % propylene; about 0.1 to about 20 wt % branched olefin; and the copolymer having a weight average molecular weigh of about 80,000 to about 800,000 Daltons, wherein a weight average molecular weight of the copolymer after being irradiated at a dosage of at least about 5 kGy is greater than or equal to about 90% the weight average molecular weight of the copolymer prior to being irradiated. Uses of the copolymer and a process of making the copolymer are also disclosed.