Microkinetics of crystallization and melting behavior of solid-state polymerized poly(ethylene terephthalate) (PET)

The microkinetics of crystallization and the melting behavior of solid-stat e polymerized poly(ethylene terephthalate) (PET) have been studied. After c orrelating crystallization data with secondary nucleation theory and a sing le regime of growth, a positive correlation was found between molecular wei ght, free energy products, and transport activation energy. The results ind icate that the crystallization behavior of PET might be correlated with reg ime III if the secondary nucleation theory is assumed to apply. They also s upport a model of crystallization involving primary and secondary crystalli zation with increased branching when the molecular weight increases. The me lting behavior of PET, previously studied at commercial levels of molecular weight, and proposed before as morphologically the reverse of the crystall ization process (Medellin-Rodriguez et al. J Poym Sci B Polym Phys 1997, 35 , 1757), continues with solid-state polymerized PET. In particular, it was observed that the second melting endotherm continues to increase with the m olecular weight, the process involving a proportional decrease of the third endotherm. This characteristic continues even up to levels where only the first and second melting endotherms are present. The first melting endother m was also studied, and the results indicated that it is probably related t o low molecular weight segregated fractions. (C) 1999 John Wiley & Sons, In c.