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

The thermal. decomposition of poly(vinyl acetate) (PVAc) in solution was in vestigated both in the presence and absence of a hydrogen donor (H-donor). Thermal degradation experiments at 220-250 degreesC were conducted in a bat ch reactor by dissolving PVAc in diphenylether. The molecular weight distri butions were measured as a function of reaction time. Experimental data ind icated that the polymer degrades by random chain scission. The random sciss ion degradation rate coefficient was between 9.01 x 10(-4) and 6.12 x 10(-3 ) min(-1). The activation energy, determined from the temperature dependenc e of the rate coefficient, was 31.5 kcal/mol. The effect of an H-donor, dip henylamine, 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 x 10(-3) to 4.59 x 10(-3) min(-1) at 24 0 degreesC. This is in contrast to the reduction in the degradation rate of polystyrene in the presence of diphenylamine. Continuous distribution mode ls have been developed by treating molecular weight as a continuous variabl e. The experimentally observed variation of the degradation rates with H-do nor concentration is satisfactorily explained by a continuous distribution model based on the radical mechanism that involves the elementary reactions including the hydrogen abstraction steps. (C) 2001 John Wiley & Sons, Inc.