Polyester–polycarbonate blends. I. Poly(butylene terephthalate)

Melt blends of bisphenol A polycarbonate with poly(butylene terephthalate) were studied by DTA and dynamic mechanical behavior to determine their state of miscibility. Both techniques showed multiple glass transitions indicative of incomplete miscibility in the amorphous phase. However, these transitions in some cases did not correspond to those in the pure components and varied with overall blend composition in some instances. This indicates that there are amorphous phases containing both components, i.e., partial miscibility. This view was supported by the crystallization behavior of the polyester. Two crystallization exotherms were observed for quenched samples, which is interpreted as polyester crystallization from two separate phases, one richer in this component than the other. Other interpretations of these results are discussed.