Mathematical models of the initial stage of the thermal degradation of poly(vinyl chloride)—3. The thermal degradation of poly(vinyl chloride) in the presence of HCl

Abstract

Several mathematical models for the initial stage of the thermal degradation of PVC in the presence of HCl which, are concerned with the different mechanisms of the autocatalytic degradation of PVC have been considered. In two cases agreement of the theoretical kinetic curves of PVC dehydrochlorination with the experimental ones was observed: (i) HCl accelerates the thermal degradation of normal units of macromolecules by the molecular mechanism; (ii) autocatalytic degradation of PVC is the branched chain reaction with degenerative branching of chain. The products of the thermal degradation of PVC (polyene and HCl) interact with each other and produce new active species which cause additional initiation of the thermal degradation of normal units of PVC by a chain mechanism. The mathematical models for the thermal degradation of PVC in the presence of HCl and active dienophil (maleic anhydride) have been proposed. The results obtained and the literature data concerning the thermal degradation of PVC in the presence of HCl have allowed the supposition to be drawn that the autocatalytic degradation of PVC is a branched chain reaction with degenerative branching of chain.