Primary photochemical processes in UV-irradiated poly(vinyl chloride) and chlorinated PVC

Abstract

The kinetics of the photodegradation of poly(vinyl chloride) and of chlorinated PVC films were studied both in the presence and in the absence of oxygen and quantum yields Φ of the major photochemical processes were determined. Dehydrochlorination develops more intensively in chlorinated PVC than in PVC, leading to long polyene sequences which are responsible for the rapid discoloration of the irradiated film. Φ values indicate that only a small fraction of the photons absorbed induces the polymer degradation. In the photooxidation of PVC and of chlorinated PVC two radicals play a predominant role: (1) the β-chloro-alkyl radical which, by splitting off the β chlorine, initiates the zip-dehydrochlorination, and (2) the γ-chloroperoxy radical which is responsible for the production of carbonyl and hydroperoxide groups as well as for the chain scissions and crosslinks. The reasons for the higher photosensitivity of chlorinated PVC are discussed and an overall reaction scheme is suggested for each polymer.