THE INFLUENCE OF MOLECULAR WEIGHT ON THE REGIME CRYSTALLIZATION OF POLY(TRIMETHYLENE TEREPHTHALATE)

Abstract

An optical microscope equipped with a video photography system was used to monitor the spherulite growth of poly(trimethylene terephthalate) (PTT). The thermal stability of PTT in nitrogen atmosphere was assessed from the variations of the growth rates of spherulites at 180 and 190°C after the samples were equilibrated for 5 or 6 min at melting temperatures in the range of 270–305°C. The growth rates remained nearly constant for melting temperatures up to 290°C and then increased with increase in melting temperature. It is suspected that degradation and transesterification occur in PTT at high temperatures in the melt. Results in this study suggest that when the melt of PTT has been equilibrated at 290°C for 5 min in nitrogen, the subsequent crystallization behavior is nearly independent of the prior thermal history. Linear growth rates of crystallization were then measured in the temperature range of 165–218°C for the PTT samples with three different molecular weights. Kinetic analysis indicated that PTT exhibits a regime transition which appears to be dependent on the molecular weight, decreasing with increase in molecular weight. The effect of equilibrium melting temperature on the product of lateral and fold surface free energies, σσ e, and the transition temperature will be discussed.