MICROPHASE SEPARATION AND RHEOLOGY OF A SEMICRYSTALLINE POLY(ETHER-ESTER) MULTIBLOCK COPOLYMER

A microphase separation transition (MST) of a thermoplastic elastomer based on soft segments of poly(tetra methylene oxide) and hard crystal line segments of poly( tetra methylene terephthalate) has been studied by means of rheological measurements, differential scanning calorimet ry (DSC), and wide-angle X-ray scattering (WAXS), showing that the MST is entirely caused by melting/crystallization, and that no separate s egmental mixing/demixing transition is involved. DSC and WAXS measurem ents show that melting starts at 190 degrees C, leading to crystal reo rganization effects up to above 200 degrees C, and that a gradual decr ease in crystallinity occurs from below 210 degrees C up to 224 degree s C, above which temperature no crystals are left. Rheological measure ments reveal a wide MST (207-224 degrees C) upon heating, which coinci des perfectly with the melting range. From this coincidence together w ith the Maxwell fluid behavior directly following the MST, it is concl uded that melting leads to a one-phase liquid, and that no separate se gmental mixing transition occurs. Similar results are obtained upon co oling, indicating that crystallization is the driving force for phase separation and that no separate segmental demixing step precedes cryst allization. The wide MST implies a large processing window over which the rheological properties change from highly elastic, with a distinct yield stress, to normal pseudoplastic, enabling application in prepar ation of structured blends. (C) 1998 John Wiley & Sons, Inc.