Reaction kinetics for solid-state polymerization of poly(ethylene terephthalate)

A simple kinetic model capable of describing the behaviors of solid-state polymerization (SSP) of poly(ethylene terephthalate) (PET) has been developed. According to this model, there are two types of end groups, namely active end groups and inactive end groups, and the solid-state polycondensation reaction is a second-order reaction with respect to the active end group concentration. The inactive end groups include chemically dead end groups and functional end groups that are immobilized by the crystalline structure. The inactive end group concentration determines the ultimate intrinsic viscosity (TV) or molecular weight achievable in the SSP-the lower the inactive end group concentration, the higher the ultimate IV. Four pulverized PET prepolymers with IV values ranging from 0.20 to 0.35 dL/g were solid-state polymerized in a fluid-bed reactor at temperatures between 200 and 230 degreesC to generate data to test the model. The experimental results fit the proposed rate equations very well, confirming the adequacy of the proposed kinetic model. Under these SSP conditions, the activation energy is about 23.6 kcal/mol and the average SSP rate about doubles with each 10 degreesC increase in temperature. The rate constant increases, while the inactive end group concentration decreases, with increasing temperature and prepolymer IV. This explains why the reaction rate and the ultimate IV increase with increasing prepolymer IV as well as temperature in the SSP of PET. (C) 2001 John Wiley & Sons, Inc.