DEGRADATION AND STABILIZATION OF POLY(VINYL CHLORIDE) .3. CORRELATIONOF ACTIVATION ENTHALPIES AND ENTROPIES FOR DEHYDROCHLORINATION OF CHLOROALKANES, CHLORALKENES AND POLY(VINYL CHLORIDE)

Activation enthalpy-entropy correlations far the experimental data ava ilable for dehydrochlorination of chloroalkanes and chloroalkenes in t he gas and in the liquid phase or non-polar solvents show that this re action has two possible mechanisms: chloroalkanes, 3-chloro-1-alkenes (drop CH-CHCl-CH=CH2,) and trans 1-alkyl-3-chloro-1-alkenes (drop CH-C HCl-CH=CH-CH drop) (gas phase) eliminate HCl through a transition stat e of four centers requiring a synperiplanar conformation of the drop C H-CCl drop group (Scheme 1). Cis 1-alkyl-3-chloro-1 -alkenes (drop CH- CHCl-CH=CH-CH drop ) and trans 1-alkyl-3-chloro-1-alkenes (liquid phas e) and conjugated 1-alkyl-5-chloro-1,3-alkadienes (drop CCl-CH=CH-CH=C H-) eliminate HCl through a transition state of six centers requiring a cis configuration of the double bond (Scheme 2). The activation para meters for the elementary reactions of PVC degradation fit on the same correlation lines supporting, for the initiation reaction, a mechanis m involving a transition state of four centers and for propagation and termination reactions, a mechanism involving a transition state of si x centers.