Mechanism of peroxidation of solid polymers as derived from the kinetics of the induced graft copolymerization

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Abstract
Grafting of acrylonitrile onto various radiation peroxidized polymers was used as a technique to investigate the peroxidation mechanism. It was found that in polymers such as polypropylene, poly(vinyl chloride), and polystyrene, a chain hydroperoxidation process only occurs above the glass transition temperature of the polymer. In the vitreous state, the polymer peroxidizes much more slowly via a single step radical‐radical combination process. In polyethylene and cellulose triacetate, a chain hydroperoxidation reaction is also observed at elevated temperatures, but the chain process is stopped at a critical temperature, which is dependent on the radiation intensity. It is shown that this effect can be interpreted, assuming that radical‐radical combination then efficiently competes with chain propagation. A discussion of the results shows that a polymer is likely to suffer more severe oxidation than a mobile liquid of similar chemical structure, owing to the much slower radical‐radical combination process in the viscous medium of the polymer.