Crystallization characteristics of weakly branched poly(ethylene terephthalate)

A series of branched poly(ethylene terephthalate) (BPET) samples were prepared from melt polycondensation by incorporation of various amount (0.4-1.2 mol%) of glycerol as a branching agent. These polymers were characterized by means of H¹ NMR, intrinsic viscosity. The general crystalline and melting behavior was investigated via DSC. It was found that the crystalline temperature T_cc from the melt shifted to high temperature and the T_hc from the glass got low for BPETs while the melting temperatures of BPETs kept almost unchanged. The kinetics of isothermal crystallization was studied by means of DSC and POM. It was found that the present branching accelerated the entire process of crystallization of BPETs, although prolonged the induced time. In addition, branching reduced nucleation sites; hence the number of nucleates for BPET got smaller. Therefore, more perfect geometric growth of crystallization and greater radius of spherulites could develop in BPET due to less truncation of spherulites.