Radiation chemistry of polyethylene. XIV. Allyl radical decay kinetics in different types of polyethylene

Abstract

AbstractThe decay kinetics of the chain allyl free radical has been studied in the following morphological forms of polyethylene (PE): Marlex bulk film, hydrogenated PE, and extended‐chain PE. Coupled with previous work on single‐crystalline PE it can be seen that the decay rate is greater the more amorphous the sample. In the Marlex bulk film and hydrogenated PE the decay can be interpreted in terms of a simultaneous fast and slow decay process by means of our Q‐function equation, but with rising temperature the decay approximates a single rate process. With extended‐chain PE the allyl decay rate does not become appreciable until the melting range is approached. The fraction of allyl radicals decaying by the slow process is 2 to 10 times greater than the fraction of fast decaying radicals. The ratio of the fast decay rate constant to that of the slow rate constant is greater for the bulk Marlex film than for the hydrogenated PE. All ratios decrease with rising temperature. For times up to about 150 min the allyl decay in the extended‐chain PE accurately follows a single second‐order decay law with a time‐independent diffusion controlled reaction rate constant.