A mathematical model of the melt transesterification of polycarbonate in a mechanically agitated reactor system without a distillation column is proposed. Penetration theory is applied to the mass-transfer operation of volatile components in both a transesterification. reactor and a polymerization reactor by simplification of the flow pattern. The applicability of the proposed model is examined by the comparison of its predictions with experimental data of the collected condensate of volatile components, the end-group ratio, and the weight fraction distribution of the resulting polymer. The end-group ratios have been determined by carbon-13 nuclear magnetic resonance spectroscopy, and the distribution of weight fractions has been measured by gel permeation chromatography. It is shown that the model's predictions are very consistent with the experimental data. (c) 2008 Wiley Periodicals, Inc.