Blends of amide modified polybutylene terephthalate and polycarbonate: phase separation and morphology

Blends are made of polycarbonate (PC) and poly(butylene terephthalate) (PBT) or amide modified poly(butylene terephthalate) (PBTA). The blends were prepared by melt blending. The blend morphology was studied by transmission electron microscopy. The PC phase was stained with RuO4. The particle sizes in the PC/PBT blends are small (less than 0.5 mu m) and the particle sizes in the PC/PBTA blends are larger (0.5-5 mu m) The blends were stabilized against transesterification by inactivation of the titanate catalyst in the PBT/PBTA with triphenyl phosphite (TPPi). A side effect of TPPi is that it acts as a plasticizer for the PC phase. The results were corrected for this effect. Also studied are the influence of the amide concentration in the PBTA from 0% (PBT) to 25 mol% (PBTA25) and the concentration of PBT(A) in the PC/PBT(A) blend over the whole composition range on the glass transition temperature (T-g) of the PC phase of the blend. Also studied are the crystallization behaviour as function of PC/PBT(A) composition and the phase separation on annealing. The PC/PBT blends were found to be partially miscible. As a result of this, the T-g of the PC was lowered and the crystallization of PBT slowed down. The PC/PBTA blends with 20-25 mol% amides in the PBTA were immiscible. The crystallization rate of the PBTA was high, and was not affected by the presence of the PC. The blends with PBTA had a higher melting temperature, were faster crystallizing, and had a higher T-g of the PC phase. (C) 1997 Elsevier Science Ltd.