Studies on the melt transesterification of DPC and BPA for synthesis of polycarbonate

The catalytic reaction of the melt transesterification of diphenyl carbonate (DPC) and bisphenol-A (BPA) is investigated theoretically. A reaction mechanism based on the nucleophilic substitution on the carbonyl group of reactants is proposed for the description of the kinetic behavior of the reaction under consideration. The applicability of the present model is justified by fitting it to the available experimental data reported in the literature, and its performance is found to be satisfactory for a wide range of operating conditions. The transesterification of DPC and BPA is of reversible nature; the forward reaction is second order in the concentrations of DPC and catalyst, and the reverse reaction is third order in the concentrations of phenol, oligomer, and catalyst. The synthesis of polycarbonate (PC) by the melt transesterification using 4-dimethylamino pyridine (DMAP) as the catalyst was studied experimentally. The monomer ratio markedly influenced the intrinsic viscosity of the resulting polymer. A ratio in the range 1.03-1.05 was found to yield polymer with a high intrinsic viscosity. The molecular weight distribution of the PC was with the most probable distribution. The concentration of the catalyst reasonably affected the hue of the PC resin, and we suggest that it should not to exceed 50 ppm when DMAP is used as the catalyst. Also, a mathematical model was of the melt transesterification of polycarbonate in a mechanically agitated reactor system, was proposed. The ideal penetration theory was applied to the mass-transfer operation of volatile components in both a transesterification reactor and a polymerization reactor by simplifying the flow pattern. The applicability of the proposed model was examined by comparing its predictions with experimental data. NMR measurements support the predicted end-group ratio of the resulting polymer. The predicted distribution of weight fractions is well matched to the profiles measured by GPC.