| Abstract: | Rates of oxygen absorption and formation of oxidation products were determined in γ-initiated oxidations of thin films of high- and low-density polyethylene, atactic and isotactic polypropylene, and of three ethylene–propylene copolymers. Radiation yields G for O2 absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallinity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene–propylene copolymer, initiated by di-tert-butylperoxy oxalate, indicate that 37 mole-% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking. |
