DEGRADATION AND STABILIZATION OF POLY(VINYL CHLORIDE) .2. 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 intermediat es with an increasing number of double bonds. Each of these intermedia tes partitions between a relatively stable polyene (termination reacti on) and the next intermediate of the chain (propagation reaction) (Sch eme 1). Experimental time dependencies of hydrochloric acid evolution, rates of polyene sequence and benzene formation in solid PVC degradat ion, data from the previous paper of this series, were simulated using a simplified model (Scheme 2). Mean rate constants and activation par ameters for random initiation, propagation and termination reactions o f the PVC degradation chain were calculated. All three types of reacti ons have low activation enthalpies and entropies suggesting concerted hydrogen chloride eliminations.