Degradation and stabilization of poly(vinyl chloride). II. Simulation of the poly(vinyl chloride) degradation processes initiated in the polymer backbone

The thermal degradation of PVC consists of a slow initiation followed by a chain of fast reactions generating a series of active intermediates with an increasing number of double bonds. Each of these intermediates partitions between a relatively stable polyene (termination reaction) and the next intermediate of the chain (propagation reaction) (Scheme 1). Experimental time dependencies of hydrochloric acid evolution, rates of polyene sequence and benzene formation in solid PVC degradation, data from the previous paper of this series, were simulated using a simplified model (Scheme 2). Mean rate constants and activation parameters for random initiation, propagation and termination reactions of the PVC degradation chain were calculated. All three types of reactions have low activation enthalpies and entropies suggesting concerted hydrogen chloride eliminations.