Synthesis of polycarbonate by melt transesterification process

Polycarbonate is synthesized by melt transesterification of diphenyl carbonate (DPC) with bisphenol A (BPA). The catalytic activity of metal acetylacetonates and the effects of the stronger or weaker bond between the catalyst and the reactant, catalyst concentration, initial monomer molar ratio, initial pressure and temprature are investigated. The logarithms of the stability constants (lgβ1) of dibenzoyl methane (DBM) complexes of the corresponding metal species are regarded as corresponding to the bond strength between metal species (catalyst) and benzoyl group (reactant) ,which are correlated by double volcanoes-shaped relationship with the intrinsic viscosity ([η]) of the PC produed with the corresponding metal acetylacetonates as catalysts. Consequently, the catalytic activity of the metal compounds is affected by the basic of acetylacetonate anion and the chelating capacity of each metal species, which is found to be very useful in forecasting the catalytic activity of the metal compound. In all the catalysts, lithium acetyacetonate (Li AC AC) is the best one, by which the sample catalyzed has the lowest fries level and polydispersity index (PDI=2.12), besides its colorless and high molecular weight ([η]=0. 710 dL · g-1 ). Our study exhibites that the best reagent molar ratio: nBPA : n DPC : nLiACAC = 1.0 : 1.08 : 1.5 X 10-4, the optimal initial pressure in the transesterification stage; 4000 Pa and the optimal melt polymerization temperature 260 °C.