Composition and crystallinity effects in the degradation of ethylene-propylene copolymers by γ-radiation

The degradation by γ-radiation of amorphous ethylene-propylene (EP) copolymers containing 23 and 36% propylene has been studied by measuring the yields of radical intermediates (at 77 K), volatile products (H2 and CH4 at 300 K), and main-chain scission and crosslinking. The G values for these changes in the homopolymers polyethylene (PE) and polypropylene (PP) all increase with decreasing crystallinity. The values for the amorphous EP copolymers are much lower than would be predicted by linear extrapolation of the values for PE and PP of low crystallinity. We conclude that all of these radiation-induced chemical changes in polyolefins occur preferentially at crystalline surfaces and defects; consequently the G values will be lower for both highly crystalline and amorphous polymers than for polymers of low crystallinity