Melt polymerization of bisphenol-A and diphenyl carbonate in a semibatch reactor

The effect of thermodynamic phase equilibrium on the kinetics of semibatch melt polycondensation of bisphenol-A and diphenyl carbonate was studied for the synthesis of polycarbonate. In the melt-polymerization process, a part ial loss of diphenyl carbonate occurs as the reaction by-product phenol is removed from the reactor. To obtain a high molecular weight polymer under h igh temperature and low-pressure conditions, a stoichiometric mol ratio of the two reactive end groups needs to be maintained during the polymerizatio n. In this work, vapor-liquid equilibrium data for a binary mixture of phen ol and diphenyl carbonate are reported and they are used in conjunction wit h the Wilson equation to calculate the exact amounts of diphenyl carbonate and phenol returned from a reflux column to the reactor. A good agreement b etween the reactor model simulations and the experimental polymerization da ta was obtained. It was also observed that diphenyl carbonate is quickly co nsumed during the early stage of polymerization and the fraction of evapora ted diphenyl carbonate refluxed to the reactor is essentially constant duri ng this period. (C) 2001 John Wiley & Sons, Inc.