The solid-state polymerization (SSP) reaction kinetics of poly(ethylene terephthalate) were investigated in connection with the initial precursor intrinsic viscosity (IV; molecular weight). Evaluations were performed with otherwise equivalent precursors melt-polymerized to IVs of 0.50, 0.56, and 0.64 dL/g. The changes in the molecular weight and other properties were monitored as functions of the reaction times at solid-state temperatures of 160-230degreesC. Precursors with higher initial molecular weights exhibited higher rates of SSP than those with lower initial values, as discussed in connection with the levels of crystallinity and the carboxyl and hydroxyl end-group composition. Activation energies decreased at temperatures above 200degreesC, and this indicated a change in the SSP reaction mechanism. At temperatures of 200-230degreesC, similar activation energies were required for the polymerization of all three precursors. Lower temperature polymerizations, from 160 to 200degreesC, required higher activation energies for all precursors, with the 0.50-IV material requirement almost twice as high as that calculated for the higher IV precursors. (C) 2003 Wiley Periodicals, Inc.