Studies of the Structure and Shape Memory Effect of Segmented Polyurethane Ionomer.

摘要

Shape memory polyurethane (SMPU) is composed of the reversible phase and the fixed phase. Usually, the hard segment content, the soft segment length and the molecular structure are paramount on controlling the shape memory property in general. However, increasing the hard segment content provides an option to alter their inter-connectivity at the expense of the crystallizable soft segment content, and thus lowering the shape fixity ratio. The chemical cross-linking hard segment structure, incorporated into SMPU to improve its shape memory function, will cause the loss of reprocessing ability of this originally thermal plastic polymer. Therefore, in this study, the Coulombic force produced by ionic groups within hard segments was considered as an adjustable internal force of the fixed phase, with which the processing ability of thermal plastic segmented PU can be kept.;For the above purposes, several series of SMPU anionomers and cationomers with various ionic group contents were synthesized and analyzed. Considering the huge influence of soft segment crystallization on shape memory effect, the isothermal crystallization kinetic method was conducted with DSC to investigate the crystallization mechanism and process in SMPU ionomers. Microstructure and properties of SMPU ionomers were investigated by using DSC, DMA, FTIR, POM, Instron universal tensile tester.;Result shows that ionic group contents have significant effect on the morphology of SMPU ionomers, accordingly affect the shape memory properties. The ionic groups within hard segments play the two-fold effect: (i) the disruption of the order of hard domain, and (ii) the enhancement of cohesion among hard segments. The former effect can be detected from the decrease of elastic modulus plateau in temperature higher than transition temperature, subsequently, the recovery ratio presents decreasing trend. The latter effect can be observed from the comparison of DMA results between SMPU ionomers and non-ionomers.