Boiling water aging of a miscible blend of polycarbonate and a copolyester

Extruded films and injection molded bars of a copolyester based on 1,4‐cyclohexanedimethanol condensed with a mixture of isophthalic and terephthalic acids, of a bisphenol‐A based polycarbonate, PC, and of the miscible blends of these compounds were exposed to boiling water for up to 15 days. The ductility and strengths of film specimens rich in PC were found to degrade as a result of PC hydrolysis. These properties of specimens rich in copolyester were found to decline as a result of crystallization of the copolyester. Best overall performance was obtained for 50/50 blends of PC and copolyester. All amorphous materials showed a transition from ductile to brittle behavior at the same weight average molecular weight as previously observed for pure PC. This feature plus the observation that PC hydrolyzes in the blend at the same rate as it does in the pure state allows most of the superior performance of the 50/50 blends to be explained in terms of blend molecular weight.