A DSC STUDY OF MISCIBILITY AND PHASE-SEPARATION IN CRYSTALLINE POLYMER BLENDS OF PHENOLPHTHALEIN POLY(ETHER ETHER SULFONE) AND POLY(ETHYLENE OXIDE)

The miscibility of blends of phenolphthalein poly(ether ether sulfone) (PES-C) and poly(ethylene oxide) (PEG) was established on the basis o f the thermal analysis results. Differential scanning calorimetry (DSC ) studies showed that the PES-C/PEO blends prepared by casting from N, N-dimethylformamide (DMF) possessed a single, composition-dependent gl ass transition temperature (T-g), and thus that PES-C and PEO are misc ible in the amorphous state at all compositions at lower temperature. At higher temperature, the blends underwent phase separation, and the PES-C/PEO blend system was found to display a lower critical solution temperature (LCST) behavior. The phase separation process in the blend s has also been investigated by using DSC. Annealed at high temperatur es, the PES-C/PEO blends exhibited significant changes of thermal prop erties, such as the enthalpy of crystallization and fusion, temperatur es of crystallization and melting, depending on blend composition when phase separation occurred. These changes reflect different characteri stics of phase structure in the blends, and were taken as probes to de termine phase boundary. From both the thermal analysis and optical mic roscopy, the phase diagram of the blend system was established. (C) 19 97 John Wiley & Sons, Inc.