Comprehensive modeling studies were used to describe the kinetics of the solid-state polymerization (SSP) of poly(ethylene terephthalate). The validity of the model was confirmed by the successful fitting of the experimental results for molecular weight increases, at temperatures ranging from 180 to 230degreesC and for times up to 12 h, with one fitting parameter. The changes in the concentrations for hydroxyl end groups ([-OH]), carboxyl end groups ([-COOH]), vinyl end groups, and terephthalic acid (TPA) were simulated with the model. During SSP, the contents of not only hydroxyl and carboxyl end groups but also vinyl ester end groups and TPA monomer were predicted to decrease as a function of the SSP time and temperature. The effects of the pellet size and the molar ratio of carboxyl end groups to hydroxyl end groups were also calculated. At an end-group molar ratio ([-COOH]/[-OH]) of around 0.7, a maximum SSP rate was obtained. As the [-COOH]/[-OH] ratio increased, the contents of the vinyl end groups and TPA monomer were predicted to increase. (C) 2003 Wiley Periodicals, Inc.