The influence of soft segment length on structure and properties of poly(trimethylene terephthalate)-block-poly(tetramethylene oxide) segmented random copolymers

Two series of multiblock poly(ether-ester)s based on poly(trimethylene terephthalate) (PTT) as the rigid segments and poly(tetramethylene oxide) (PTMO) as the flexible/soft segments were synthesized with the aim of developing of the new family polyester thermoplastic elastomers (TPEs) based on PTT as rigid segment. The content of PTMO segments in the polymer chains was varied from 20 to 80 wt%. The investigations were mainly focused on the influence of flexible segments length with starting PTMG molecular weight at 1000 and 2000 g/mol, respectively, on the phase structure, thermal and mechanical properties of resulting copolymers. The copolymers were characterized by Size Exclusion Chromatography (SEC), Differential Scanning Calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), Wide-angle X-ray scattering (WAXS), Small-angle X-ray scattering (SAXS), and other standard physical methods. Cyclic tensile properties of them were studied with the aim to evaluate the elastic properties. SEC results clearly demonstrated the formation of molecular weight segmented copolymers with microphase separated structure as denoted by DSC and DMTA. The enhanced phase separation was observed for copolymers containing longer flexible segments. According to the characterizations, copolymers containing 50-80 wt% of flexible segments showed elastic behavior. Comparison of the values of permanent set for copolymers with shorter and longer flexible segments has shown that copolymers containing 30 and 40 wt% of long PTMO flexible segments have the best elastic properties (low permanent set). Copyright (C) 2010 John Wiley & Sons, Ltd.