Study on the liquefied-MDI-based shape memory polyurethanes

A series of liquefied-MDI-based polyurethanes having shape memory behavior, with various soft segments, chain extenders, and micro-phase separation promoters were synthesized. Their morphology and properties were investigated in terms of thermal properties, dynamic mechanical properties, and shape recovery behavior. The results indicate that the soft segment formed with longer chain segment incline to crystallize during the cooling scans and the resulting SMPU have the higher crystallinity. Meanwhile, the chain extenders, which can enhance the polarity of hard segment, incline to have excellent shape memory properties with bigger storage modulus in rubbery state too. It was also found that the micro-phase separation promoters have great influence on the shape memory behavior due to the enhancement of micro-phase separation of SMPU. Furthermore, it was proved again that SMPU with longer soft segment and lower hard segment contents usually showed good shape memory behavior.