PHOTOOXIDATION OF POLY(VINYL CHLORIDE) .2. A COMPARATIVE-STUDY OF THE CARBONYLATED PRODUCTS IN PHOTOCHEMICAL AND THERMAL OXIDATIONS

An analytical study of the thermo-oxidation of poly(vinyl chloride), carried out at moderate temperatures (< 140-degrees-C), is reported. Changes in UV-visible and IR spectra are described. Polyene formation is observed in conditions of deoxygenated treatment and these polyenes are readily oxidized in the presence of oxygen. The oxidation products of polyenes which are obtained are shown to be the only products detected by IR analysis of thermo-oxidized samples. The mechanism of thermo-oxidation thus appears to be different from the mechanism of photo-oxidation. The reason for the observed difference is related to the different behaviours of chlorine atoms formed in thermo- and photo-oxidation: in thermo-oxidative conditions, a cage reaction that leads to the formation of polyenes is favoured. In photo-oxidation, the ejection of chlorine atoms occurs, leading to the initiation of a random oxidation of normal structures.