TRANSESTERIFICATION IN BLENDS OF POLY(BUTYLENE TEREPHTHALATE) AND BISPHENOL-A-POLYCARBONATE

By means of differential calorimetric and X-ray examinations it was shown that poly(butylene terephthalate) (PBT) and bisphenol-A-polycarbonate (PC) are only compatible in the melt if they stay in the melt for a short period of time. During mixing in the melt, transesterification begins and block copolymers are formed. A characteristic glass transition temperature is observed for each individual blend. Butylene terephthalate (BT)-blocks are crystallizable; however, with an increasing share of bisphenol-A-carbonate (BPAC) the specific melting enthalpy of the BT-blocks decreases. Within copolymers with a high BPAC content, the BPAC segments crystallize considerably faster than in pure PC. By means of diffraction measurements with synchrotron radiation, the mechanism of stress-induced alpha-beta-modification change in pure PBT and in block copolymers with high BT-contents could be explored.