Influence of tacticity on the thermal degradation of PVC: 8. A comprehensive study of the local isotactic GTTG− conformation dependence of the mechanism of initiation

Abstract

Some new attempts to demonstrate the superiority of the GTTG − conformation of isotactic triads relative to other labile structures containing allylic or tertiary chlorine in inducing the thermal degradation of poly(vinyl chloride) (PVC) are presented. They concern: (i) the degradation of polymers after nucleophilic substitution in two types of solvent involving the removal of the GTTG − arrangement in a quite different way; (ii) the degradation of PVC blends with a few additives which, as proved by Fourier transform infrared ( FTi.r.) spectroscopy, are able to interact specifically with the mmr structure adopting GTTG − TT conformation at the end of isotactic sequences; (iii) the degradation of PVC after the disappearance of GTTG − conformations as a result of the GTTG − TT x → GTGTTT irreversible conformational change provoked by stretching of films at temperatures near the glass transition; and (iv) the degradation of PVC after FTi.r. checked changes in content of GTTG − conformation, induced by annealing at temperatures between 70 and 120°C. The correlations so obtained give evidence of the PVC thermal-instability-determining role of the GTTG − isotactic triad conformation.