Water sorption and hydrolytic stability of polycarbonates

The hydrolytic stability of a new commercial polycarbonate (Calibre 300, Dow Chemical USA) was investigated and compared with that of other commercial polycarbonates. The tests were conducted between 56% and 95% relative humidity (R. H.) at 100°C. Also performed were water immersion tests at 80 and 100°C. The water diffusivity was found to be 8.7 × 10−7 cm2/s at 100°C with an activation energy of 7.9 kcal/mole. These values are similar to other glassy polymers. The equilibrium water sorption, C∞, was found to increase with temperature and R.H. The isotherm at 100°C was determined to be: C∞ = 0.005945 [R.H.]. When samples immersed in a water bath at 100°C were transferred into room‐temperature water, visible aqueous microcavities were formed due to the condition of super‐saturation, and under stress may become crack initiation sites. For the polycarbonate investigated here, it was found that the decrease in weight‐average molecular weight (M̄)w was a first‐order process under a constant R.H. and temperature, and that hydrolytic embrittlement, i. e., (M̄)w