Gel permeation chromatography studies of chain scission and cross-linking during photo-oxidation of atactic polystyrene below and at tg

Photo-oxidative degradation of polystyrene in the form of film 20 μm thick was carried out in air using u.v. light of 254 nm at room temperature and at temperatures up to T_g. GPC was used to study changes of molecular weight distribution during the process. The GPC results were analysed using equations for an initially most probable distribution and non-uniform energy dissipation; the quantum yield values of chain scission and cross-linking of polystyrene during degradation were calculated. Initially, degradation progressed at high rate, connected with consumption of oxygen dissolved in the film. The slower subsequent degradation was connected with consumption of oxygen supplied during the reaction. An appreciable increase in the quantum yields for chain scission and cross-linking was observed just below and at T_g for the initial stage of photo-oxidative degradation. This increase of the quantum yield of photodegradation was caused by increased mobility of oxygen molecules in the film, connected with movement of polymer chain elements.