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

The main variables involved in solid-state polymerization of PET homopolyme rs, originally with molecular weight within the commercial range, were sequ entially studied to determine their influence in polymerized products. Thes e variables were precursor crystallinity, catalyst, and time and reaction t emperature. An increasing molecular weight sequence was then used to study the hulk crystallization behavior with Avrami analyses. It was determined t hat thermal conditions at dissolution affect the prereaction morphology. Th is was important in the polymerization process because it was found that hi gh crystallinity levels in precursors result in higher molecular weights. I n agreement with other reports, typical catalysts used in melt polymerizati ons enhance postpolycondensation processes in the solid state. High. reacti on times and temperatures were also required to obtain high molecular weigh ts. As the molecular weight increased, there was a decrease in nucleation d ensity and Avrami analyses, applied to the isothermal bulk crystallization, indicating that the nucleation process changed from instantaneous to spont aneous with the increase in molecular weight. The consequences and relative importance of the observed results is discussed. (C) 2000 John Wiley & Son s, Inc.