Method of preparing polycarbonate

Abstract

Polycarbonates incorporating terminal carbonate groups derived from ester-substituted activated carbonates in a transesterification process have unfavorable properties with respect to color, hydrolytic stability and thermal stability, particularly when the polycarbonate containing such end groups is molded. The number of activated carbonate end groups formed during the melt transesterification formation of polycarbonate can be reduced by reacting a dihydroxy compound with an activated diaryl carbonate in the presence of an esterification catalyst to produce a polycarbonate, in the presence of a monohydroxy chainstopper such as para-cumyl phenol in an amount that results in 35 to 65 mol % of the end groups being derived from the monohydroxy chainstopper. Suitably, the reactants are provided such that the molar ratio of activated diaryl carbonate to the total of dihydroxy compound plus ½ the chainstopping reagent that is less than 1.