Studies on blends of binary crystalline polymers. 1. Miscibility and crystallization behavior in poly(butylene terephthalate) polyarylates based on bisphenol A isophthalate

The miscibility and crystallization behavior of binary crystalline blends of poly(butylene terephthalate) [PBT] and polyarylate based on Bisphenol A isophthalate [PAr(I-100)] have been investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Both polymers were able to crystallize over a wide range of blend composition and temperature. This blend system exhibited a single composition-dependent glass-transition temperature over the entire composition range and two distinctive melting peaks in some compositions. The equilibrium melting point depressions of both PET and PAr(I-100) were observed, and the Flory-Huggin's interaction parameter of chi(12(PBT)) = -1.3 was obtained. It indicated that these blends were thermodynamically miscible in the melt. The crystallization rate of neat PAr(I-100) was very slow. However, it was much faster when the PET was added. The crystallization rate of PAr(I-100) was significantly influenced when the PET crystal was previously formed. It was not only due to the amorphous phase composition shifted to a richer PAr(I-100) content after the crystallization of PET but also to the constraint of the PET crystal phase. On the other hand, the crystallization rate of PET was reduced due to the addition of PAr(I-100).