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.