Hydrolysis of 1,4‐cyclohexanedimethanol‐based copolyester

The solid state hydrolysis of a copolyester based on a mixture of 1,4‐cyclohexanedimethanol and ethylene glycol condensed with terephthalic acid was studied at 100°C and 57 to 96 kPa water vapor partial pressure (55% to 95% relative humidity). The equilibrium water sorption in weight percent (C ∞ ) was found to be\documentclass{article}\pagestyle{empty}\begin{document}$$ C_\infty = 1.45 \times \,10^{ - 5} (P_{H_2 O} )^{1.2} $$\end{document}where P   H   2 Ois the water vapor partial pressure in kPa. For specimens 0.32‐cm thick, it took about 24 h to reach 0.9 C ∞ . The intrinsic viscosity ( IV ) was measured and used to calculate the relative change in molecular weight (M̄ w ) from the relationship IV ∝ (M̄ w ) 0.7 . The decrease in molecular weight was linear with time, and the rate of decrease was found to be proportional to C ∞ ; the empirical correlation is\documentclass{article}\pagestyle{empty}\begin{document}$$ k = 0.026 \times C_\infty $$\end{document}where the rate constant, k , is in day −1 . A decrease of 50% in M̄ w was observed after 22 days at 95% relative humidity.