The effects of transesterification on structure development in PC-PBT blends

Summary

A series of polycarbonate-poly(butylene terephthalate) (PC-PBT) blends has been formed via reactive melt-blending in a torque rheometer. The degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst. Resultant materials were characterised using DSC, DMA, FTIR and SEM. As the degree of transesterification increased composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of PC-PBT, with concomitant changes in their thermal behaviour. A corresponding transformation in materials morphology was observed: the relatively coarse structure characteristic of essentially two-phase blends, developed into a more refined structure exhibited by blends containing significant volumes of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolyesters.