Preparation of copolyestercarbonates by the bischloroformate process

A process for preparing a polyestercarbonate copolymer which is nearly devoid of diarylcarbonates and that exhibits a glass transition temperature lower than bisphenol-A carbonate homopolymer, and that shows improved processability is herein described. The desired lower Tg and improved flow can be achieved by the polycondensation of a dihydric phenol an aliphatic dicarboxylic acid and a carbonate forming reagent. In the claimed process a dihydric phenol is phosgenated to form chloroformate end-capped oligomers which are then polycondensed after the addition of a chain stopper and a carbonate forming reagent. The aliphatic dicarboxylic acid may be introduced in the beginning or after the formation of the chloroformates.