Crystallization behavior and spherulite morphology of soft and hard segments in ethylene terephthalate-?-caprolactone copolyesters

The crystallization behaviors and spherulite morphology of ethylene terephthalate-ε-caprolactone copolyesters (TCL) are investigated by differential scanning calorimetry (DSC) and polarized light microscope (PLM). The crystallization characteristics reflecting the random and segmented properties of TCL copolyesters are discussed. It is shown that for TCL copolyesters with low or high hard segment content, the soft CL segments or hard ET segments are long enough to crystallize and grow spherulites under certain appropriate conditions, and their crystallization abilities strengthen with the increasing segment sequence length. It is interesting that in TCL copolyesters, the crystallization of the soft segments requires considerably long sequence length, while the hard segments containing only one or two structural units can already crystallize and even grow spherulites. The hard segments can grow unusual spherulites at higher temperatures (or lower supercooling).