Solid-state polymerization and bulk crystallization behavior of poly(ethylene terephthalate) (PET)

The main variables involved in solid-state polymerization of PET homopolymers, originally with molecular weight within the commercial range, were sequentially studied to determine their influence in polymerized products. These variables were precursor crystallinity, catalyst, and time and reaction temperature. An increasing molecular weight sequence was then used to study the bulk crystallization behavior with Avrami analyses. It was determined that thermal conditions at dissolution affect the prereaction morphology. This was important in the polymerization process because it was found that high crystallinity levels in precursors result in higher molecular weights. In agreement with other reports, typical catalysts used in melt polymerizations enhance postpolycondensation processes in the solid state. High reaction times and temperatures were also required to obtain high molecular weights. As the molecular weight increased, there was a decrease in nucleation density and Avrami analyses, applied to the isothermal bulk crystallization, indicating that the nucleation process changed from instantaneous to spontaneous with the increase in molecular weight. The consequences and relative importance of the observed results is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 78–86, 2000