Comparison of shape memory polyurethanes and polyurethane-ureas having crystalline reversible phase

Abstract

Shape memory polyurethanes (SMPUs) have been extensively investigated but shape memory polyurethane-ureas (SMPUUs) with aromatic diamines as chain extenders have been rarely reported. In the present study, a series of SMPUs and SMPUUs having crystalline reversible phase were prepared. The shape memory properties including shape recovery, shape fixity and recovery stress of the SMPUs and the SMPUUs were compared systematically. When hard-segment content (HSC) was 30% the polyurethane-urea exhibited higher shape recovery than its polyurethane analogue. With the increase of HSC the shape recoveries of both the SMPUs and the SMPUUs decreased but those of the SMPUUs decreased more apparently. When HSC was 40%, the shape recovery of the polyurethane-urea was lower than that of the polyurethane. This is because the great increase of physical cross-linking density of SMPUUs resulted in significant increase of irreversible deformation. In comparison with those of the SMPUs, the shape recovery curves of SMPUUs shift to lower temperatures. This is because the higher physical cross-link density of the SMPUUs results in more decrease of the melting temperature of soft phase. Moreover, the shape fixities of the SMPUUs were lower than those of the SMPUs with identical HSC also because of their higher physical cross-link density. The recovery stresses of the SMPUs and the SMPUUs increased with the increase of HSC. The recovery stress of a polyurethane-urea was higher than that of its polyurethane analogue by over 100%. Hence it is possible to produce SMPUUs with much larger recovery stress and higher shape recovery without sacrificing much shape fixity by controlling appropriate HSC.