Melt polycondensation of bisphenol a polycarbonate by a forced gas sweeping process

Experimental and modeling studies are presented on the synthesis of bisphenol A polycarbonate at ambient pressure by a novel forced gas sweeping process. Unlike in the conventional high-vacuum melt transesterification process, the condensation byproduct (phenol) is removed from a highly viscous polymer melt in the forced gas sweeping process by forcing inert gas bubbles to flow through the polymer melt phase. As the inert gas bubbles rise in the melt phase, dissolved phenol molecules diffuse to the bubbles and are removed from the polymer melt, and the polymer molecular weight increases. To examine the feasibility of the proposed method, the effects of reaction temperature and gas flow rate on the polymer molecular weight were investigated at 260-280 degreesC and ambient pressure using a small semibatch laboratory reactor. It has been found that medium-range molecular weight polycarbonate can be readily prepared in a relatively short reaction time. The semibatch polymerization process is also modeled by a mass-transfer reaction model in which bubble size and bubble rising velocity are used to estimate the interfacial mass-transfer area and gas-liquid contact time. The experimental data suggest that the forced gas sweeping process can be a potential alternative to a high-vacuum melt polycondensation process for the synthesis of bisphenol A polycarbonate at ambient pressure.