Crystallization kinetics of poly(1,4-butylene-coethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(et hylene terephthalate) (PET), and their copolymers poly(1,4-butylene-co-ethy lene terephthalate) (PBET) containing 70/ 30, 65/35 and 60/40 molar ratios of 1,4-butanediol/ethylene glycol were investigated using differential scan ning calorimetry (DSC) at crystallization temperatures (T-c) which were 35- 90 C below equilibrium melting temperature T-m(o). Although these copolymer s contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to cr ystallize could be due to the similar chemical structures of 1,4-butanediol and ethylene glycol. DSC results for isothermal crystallization revealed t hat random copolymers had a lower degree of crystallinity and lower crystal lite growth rate than those of homopolymers. DSC heating scans, after compl etion of isothermal crystallization, showed triple melting endotherms for a ll these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2-2.5 for PET and 2.5-3.0 for PBT and PBETs. Analyses of the Lauritzen-Hoffman equation for DSC isothermal crystallization data reve aled that PBT and PET had higher growth rate constant G(o), and nucleation constant K-g than those of PBET copolymers. (C) 2001 Society of Chemical In dustry.