Cyclic polycarbonates by polycondensation of bisphenol A with triphosgene

Interfacial polycondensations of bisphenol A with triphosgene were conducted in the CH2Cl2/aqueous NaOH system. Four different catalysts were compared: triethylamine, triethylbenzylammonium chloride (TEBA-Cl), tetrabutylammonium hydrogen sulfate, and tetraphenylphosphonium chloride. Triethylamine yielded mixtures of cyclic polycarbonates and OH-terminated polycarbonates. The fraction of cycles and the molecular weights increased with lower concentrations of this catalyst. When the pseudo-high-dilution method was applied, samples containing greater than or equal to95 mol % of cycles were obtained, and the average molecular weights were varied over a broad range via the feed ratio of triethylamine. Fractionation of one sample allowed the detection of cyclic polycarbonates up to 28 000 Da. The three phase transfer catalysts gave quite different product mixtures when compared under identical conditions. The highest fraction of cycles and the highest molecular weights were obtained with Ph4PCl. The fraction of cycles increased with higher feed ratios of Pb4PCl in contrast to triethylamine. Bimodal mass distributions were found for all samples with a high content of cyclic polycarbonates, whereas the frequency distributions were monomodal.