The thermal degradation of polyvinylchloride in solution. I. The kinetics of the dehydrochlorination reaction

The dehydrochlorination of polyvinylchloride in ethyl benzoate solution has been studied over the temperature range 178° to 212°C in an atmosphere of nitrogen. Over this temperature range the expression for the rate in moles HCl liberated/litre. sec., is 5.7·10 7 e ‐22,800/R.T. c n , where c n is the polymer concentration in polymoles/litre. Thus, for a fixed weight concentration of polymer, the rate is inversely proportional to the number average degree of polymerisation of the polymer. The presence of oxygen does not affect the rate of dehydrochlorination, but it causes a more rapid blackening of the polymer solution, and is accompanied by chain scission. The addition of free radical initiators increases the rate somewhat while quinone type compounds have no inhibiting effect. The addition of a commercial stabilizer (Stanclere 70) containing a dialkyl tin salt resulted in a retarded rate for a period proportional to the amount added. This was followed by the normal unretarded rate. The results, however, still leave undecided the mechanism of the dehydrochlorination reaction.