Initial steps in the photolysis and photooxidation of polystyrene

Abstract

The effects of exposure of a number of differently prepared polystyrenes to long-wave u.v. ( λ ⩾ 300 nm) in O 2 were investigated. The polymers undergo two distinct phases of degradation, one associated with the initial decomposition of photo-labile structures, and the other with the photolysis of oxidation products, such as hydroperoxides. Polymers prepared under conditions of high free radical concentrations (higher temperatures and initiator concentrations) were the most reactive and contained more photo-labile structures. Hydroperoxides were prepared from these polymers and their degradations investigated. While hydro-peroxides act as initiators of the oxidative phase of the degradation, by producing radicals on photolysis, no convincing evidence was obtained for their participation in the initial photodecomposition. On the other hand, experimental data favoured the involvement of in-chain peroxides in this process. Differences of reactivity of polymer solutions and films were also observed, the apparent relative stability of films being attributed to the difficulty associated with the separation of large fragments in a more viscous medium.