Competing Cyclization and Chain Growth in tert-Amine-Catalyzed Polycondensations of Bisphenol A with Bisphenol A Bischloroformate

Abstract

Bisphenol A was polycondensed with bisphenol A bischloroformate (BABC) in CH 2 Cl 2 at 5, 20, and 40 °C using pyridine as catalyst and HCl-acceptor. The feed ratio was varied, and the maximum molecular weight was obtained with a 10 mol % excess of BABC. The MALDI-TOF mass spectra exclusively displayed peaks of cycles. Because of disproportionation of chloroformate groups, small amounts of odd-numbered cyclocarbonates were formed in addition to the prevalent even-numbered ones. Triethylamine as catalyst gave lower molecular weights, a maximum at 4 mol % excess of BABC and only traces of odd-numbered cycles. With N-ethyl diisopropylamine again, traces of odd-numbered cycles and the lowest molecular weights were obtained due to intensive side reactions. Model reactions with phenyl chloroformate and BABC indicated that pyridine catalyzes a disproportionation of chloroformate groups yielding carbonate groups in the absence of phenols or water. These polycondensations in a homogeneous organic phase yielded cyclic polycarbonates of much lower molecular weight than interfacial hydrolytic polycondensations of BABC. This finding indicates that, in contrast to comments in the literature, the interfacial polycondensations are less favorable for cyclization reactions.