| Temperature sensitive polyurethane (TS-PU) is one novel type of smart polymers. The water vapor permeability (WVP) of its membrane could undergo a significant increase as temperature increases within a predetermined temperature range. Such smart property enables this material to have a broad range of potential applications to textile industry, medicine, environmental fields and so on. However, based on the literature review, contradicting results were found on some TS-PUs. The aims of this project are to synthesize TS-PU with Tm in the broader temperature range including ambient temperature range, and then investigate systematically the relationships between microstructure and water vapor transport properties of TS-PU.; For this purpose, in this project, a series of polyurethanes (PU) were synthesized using five different crystalline polyols with approximately similar molecule weight and three different hydrophilic contents, and dense membranes were prepared accordingly. The microstructure and properties of these PUs were investigated using DSC, WAXD, DMA, FTIR, GPC, POM, TEM, SEM and PALS. Their equilibrium water sorption and water vapor permeability were measured accordingly.; Results show that crystal melting of these resulting PUs take place in the temperature range from −10–60°C as desired. Storage modulus (E′) drops down quickly in the temperature range of crystal melting, suggesting a great transition in the predetermined temperature range. The decreased HSC as well as regular chemical structure of polyols results in the larger spherulites and higher melting end temperature, and the higher crystallinity induces the more obvious incompatibility of soft segment and hard segment in the PUs. These PUs are proved to have good enough tensile properties for textile application. The mean free volume size and fractional free volume increase more significantly in the temperature range of crystal melting than in other temperature intervals.; Finally, as expected, the WVP of semi-crystalline PU membranes increases significantly in the temperature range of crystal melting. Equilibrium water sorption keeps approximately constant. The significant increase in WVP of semi-crystalline PU is obviously correlated with the sharp increase in the free volume in the predetermined temperature range. |
