Non-isothermal Crystallization Behavior of Poly(trimethylene terephthalate-co-isophthalate) Copolyesters

Poly(trimethylene terephthalate-co-isophthalate) (TI) copolyesters were synthesized using different ratios of isophthalic acid (TA) and Terephthalic acid (TPA) with 1,3-propanediol (1,3-PDO). The compositions of TI copolyesters were analyzed using H-1 nuclear magnetic resonance (NMR). Non-isothermal melt- and cold-crystallization and subsequent melting behaviors were investigated using differential scanning calorimetry (DSC). For TIO, TI10, and TI20, non-isothermal crystallization kinetics were analyzed using a modified Avrami equation. The results show that the reaction rate of TPA with 1,3-PDO was similar with that of EPA with 1,3-PDO in TI copolyesters. Crystallization exothermic peak and melting endothermic peak were not observed in DSC traces with an increase of the relative amount of P-IP, to 41%. The Avrami exponent n is in the range of 3.5-4.2 for melt-crystallized TI copolyesters and between 3.0-3.2 for cold-crystallized copolyesters. It suggests that the crystallization from melt state corresponds to thermal nucleation but the crystallization from glassy state originates from predeterminated nuclei.