Block phosphorus-containing poly(trimethylene terephthalate) copolyester via solid-state polymerization: retarded crystallization and melting behaviour

Abstract

The crystallization behavior of neat PTT and phosphorus-containing PTT copolyester with specific block chain structure (PTTDs, obtained by solid-state polymerization (SSP)) has been investigated by differential scanning calorimetry (DSC), polarized microscopy (POM) and wide-angle X-ray diffraction (WAXD). The overall crystallization kinetics study shows that crystallization is retarded with introduction of a phosphorus-containing segment. This retardation effect is obvious for PTTD10; however, no greater retardation can be observed with further increasing the phosphorus content, which is attributed to the hindering effect of phosphorus-containing segment and specific chain structure, and is in accordance with the crystallization morphology. The crystallization rate of PTTDs is much lower at high crystallization temperature than that of PTT, which can be explained by the diluent effect of the non-crystallizable chain segment. The result of spherulite growth is in accordance with DSC study. The rigid amorphous fraction (RAF) is also calculated, which increases with increasing phosphorus content, suggesting that RAF is not the main factor for retarded crystallization. The main factors of retarded crystallization are probably caused by the diluent effect and the hindering effect of the specific chain structure. With incorporation of phosphorus-containing segments, the transition temperature is slightly changed; however, the equilibrium melting temperature (T_m⁰) of the copolyester decreases. The phosphorus-containing segment plays the role of nucleation agent at regime III.