Controlled transesterification and its effects on structure development inpolycarbonate-poly(butylene terephthalate) melt blends

A series of 50:50 polycarbonate-poly(butylene terephthalate) (PC-PBT) blend s were formed via reactive melt blending in a torque rheometer. A controlle d degree of transesterification between the two homopolymers was initiated by the incorporation of an alkyl titanium catalyst during melt blending and finally quenched by the addition of a transesterification inhibitor. The r esultant materials were characterized using differential scanning calorimet ry (DSC), dynamic mechanical thermal analysis (DMTA), Fourier transform inf rared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmis sion electron microscopy (TEM). As the degree of transesterification increa sed, the composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type copolymers of PC and PBT, resulting in significant changes in their thermal behavior. A corresponding transformation in the morphology of the blends was observed due to the for mation of increasing concentrations of copolyesters. Thus, the initial coar se (>5 mu m) bicontinuous morphology developed into a more finely dispersed submicron-scale structure, exhibited by blends containing significant volu mes of interphase material; finally, at high degrees of transesterification , a homogeneous, amorphous material was formed.