The Crystalization of Soft Segment of Thermal Sensitive Polyurethane and Its Intelligent Properties
A thermal sensitive polyurethane (TSPU) membrane was prepared by two-step polymerization in solvent and the crystallization of soft segment was analyzed. The results reveal that TSPU shows an obvious phase-separated structure and a phase transition temperature of the soft segment (defined as switch temperature, Ts). The switch temperature (Ts) and the thermal sensitivity of TSPU still remain available after thermal cyclic process. Moreover, when the temperature was lower than the Ts, the crystal of the soft segment was visible, but when the temperature exceeded the phase transition temperature of soft segment, the crystal of the soft segment melted and disappeared. As a result, the average radius (R) of the free volume holes and water vapor permeability of TSPU membrane showed a response to thermal stimuli. The phase transition of the soft segment controlled the significant change in free volume hole size and WVP, and the process mentioned above was stimulated by the external temperature.
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