Effect of hydrogen donor on the thermal degradation of poly(vinyl acetate) in solution

Abstract

The thermal decomposition of poly(vinyl acetate) (PVAc) in solution was investigated both in the presence and absence of a hydrogen donor (H-donor). Thermal degradation experiments at 220-250°C were conducted in a batch reactor by dissolving PVAc in diphenylether. The molecular weight distributions were measured as a function of reaction time. Experimental data indicated that the polymer degrades by random chain scission. The random scission degradation rate coefficient was between 9.01 × 10-4 and 6.12 × 10-3 min-1. The activation energy, determined from the temperature dependence of the rate coefficient, was 31.5 kcal/mol. The effect of an H-donor, diphenylamine, was also investigated by varying the concentration from 0 to 0.472 mol/L. The data indicated that the presence of diphenylamine increases the PVAc degradation rate from 3.67 × 10-3 to 4.59 × 10-3 min-1 at 240°C. This is in contrast to the reduction in the degradation rate of polystyrene in the presence of diphenylamine. Continuous distribution models have been developed by treating molecular weight as a continuous variable. The experimentally observed variation of the degradation rates with H-donor concentration is satisfactorily explained by a continuous distribution model based on the radical mechanism that involves the elementary reactions including the hydrogen abstraction steps. © 2001 John Wiley & Sons, Inc.