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 α‐β‐modification change in pure PBT and in block copolymers with high BT‐contents could be explored.