The influence of relative humidity on polyarylate hydrolysis

The influence of relative humidity (RH), between 55 and 100%, on the rate of hydrolytic degradation of polyarylate was investigated at 100°C. The equilibrium water sorption in weight percent, C ∞ , was determined to be C ∞ = 0.0043 X (RH) 1.2 . For specimens 0.32 cm thick, it takes about 24 h to reach 0.9 C ∞ at 100°C. The decrease in molecular weight ( M̄ w ) due to the hydrolytic attack of water was linear with time, suggesting a zero‐order process with respect to M̄ w . The rate of decrease was found to be proportional to C ∞ . A 30% decrease in M̄ w was observed after 21 days at 55% RH and 100°C and, at that point, the material has become brittle.