Effect of thermal history on properties of block-copolyetheresters with poly(tetramethylene 2,6-naphthalenedicarboxylate) segments

The effect of compression molding on the thermal transitions and crystallin e properties of block-copolyetheresters with hard segments of poly(tetramet hylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethyle ne oxide) were investigated by differential scanning calorimetry (DSC), X-r ay diffraction, thermal stimulated current (TSC), and dynamic mechanical an alysis (DMA). The X-ray diffraction patterns of compression molded samples of the block-copolymers were considerably different from those of the corre sponding samples with slow-cooling history. After compression molding, the diffraction peaks were changed completely indicating a different crystallin e structure for the polyester segments, and the diffraction peaks became sh arper indicating a higher crystallinity. The DSC results also showed that t he melting point and crystallinity of the polyester segments were increased after compression molding. The glass transition temperatures of the polyet her soft phase and polyester hard phase also were determined by DSC, TSC, a nd DMA separately with consistent data and were found to be dependent on th e content of polyether segments and the molecular weight of the poly(tetram ethylene ether)glycol (PTMEG) used. A gamma-transition was observed by TSC and DMA and seemed to be independent of the composition and the thermal his tory. The glass transition temperatures of the polyether soft phase and the polyester hard phase of the bloch-copolymers derived from PTMEG 650 and PT MEG 1000 shifted to a lower temperature after compression molding possibly because of the partial miscibility between the comprising segments in these two series. The abrupt drop in log G' in the temperature range of -10-15 d egrees C for the block-copolymers derived from PTMEG 2000 was caused by the melting of the polyether segments and indicated that the crystalline prope rties of the polyether segments could affect their mechanical properties. ( C) 1999 John Wiley & Sons, Inc.