AbstractThe photodecomposition of films of poly(vinyl chloride) containing benzoyl peroxide and two aliphatic peroxides is investigated. It is proposed that the aromatic peroxide decomposed as a result of absorption of the irradiation, thus speeding up the early stages of the reaction but resulting in a lower final conversion. The aliphatic peroxides broke down as a result of energy transfer from polyenes and contributed to the propagation of the removal of HC1 with an increase in conversion. Films containing acenaphthene were ultimately more stable than the reference but decomposed faster in the early stages. It is suggested that energy transfer plays an important part in the mechanism.