Shape memory polyurethanes having crosslinks in soft and hard segments

Two types of shape memory polyurethanes (PUs) with various hard segment contents (hsc) were designed and synthesized based on the position of crosslinks, either in the soft segment or in the hard segment, and were tested for tensile cyclic loading behavior as well as mechanical and dynamic mechanical properties. It was found that hard segment crosslinks gave much smaller shape fixability and much higher shape recoverability as compared with soft segment crosslinks at the same hsc. For soft segment crosslinks, shape recovery increased as the hsc decreased, and these results could possibly be interpreted in terms of dynamic mechanical properties of the PUs, which possibly were interpreted in terms of microphase separation and crosslink density.