Miscibility and Crystallization in Binary Crystalline Blends of Poly(butylene terephthalate) with Poly(butylene terephthalate--caprolactone)

Abstract

Poly(butylene terephthalate)/poly(butylene terephthalate--caprolactone) is a new A/AxB1x binary crystalline blend with intra-molecular repulsion interaction. Using the mean-field binary interaction model, the value of interaction parameter between the butylene terephthalate and caprolactone structural unit was first reported to be 0.305. This blend exhibited different crystallization behavior from a typical homo-polymer/copolymer blend, which was carefully investigated by differential scanning calorimetry. It was found that poly(butylene terephthalate--caprolactone) copolymers have a great effect on the pure poly(butylene terephthalate) chain mobility and poly(butylene terephthalate) crystalline lattice packing. In the meantime, the crystallization of butylene terephthalate segments in copolymers was restricted by the previously formed poly(butylene terephthalate) crystallites. The two constituents for blending can not form a co-crystal in the range of composition even if they have the same butylene terephthalate unit. It can be concluded that longer segments in a copolymer would be beneficial for the formation of a co-crystal in blends.