Thermal behavior, morphology and the determination of the polymer‐polymer interaction parameter of polycarbonate‐poly(butylene terephthalate) blends

Blends of bisphenol‐A polycarbonate (PC, poly(oxycarbonyloxy‐1,4‐phenylene‐2‐isopropylidene‐1,4‐phenylene)) and poly(butylene terephthalate) (PBT, poly(oxytetramethyleneoxy‐terephthaloyl)) have been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were prepared by screw extrusion and solution casting with mass fractions of PC in the blends varying from 0,90 to 0,10. From the measured glass transition temperature (Tg) and apparent mass fractions of PC and PBT dissolved in each phase, it appears that the PBT dissolves more in the PC‐rich phase than does the PC in the PBT‐rich phase. Also, compatibility is greater in the case of extruded blends than in the case of solutioncast blends. The values of the Flory‐Huggins polymer‐polymer interaction parameter (χ12) were determined and found to range from 0,042 to 0,033 for extruded blends at 250°C and from 0,054 to 0,039 for solution casting at 25°C. The χ12 decreases with increase of PBT content throughout the investigated composition range. From the Tg's, the microscopy study and the extrudate swell ratios, it is concluded that compatibility is achieved in the blends having mass fractions 0,90, 0,20 and 0,10 of PC, but that these blends are not microscopically homogeneous.