Shape memory polyurethane-ureas based on isophorone diisocyanate

Shape memory polyurethanes (SMPUs) are usually produced with aromatic hard segments in order to ensure high shape recoverability. Here a series of non-aromatic shape memory polyurethane-ureas (SMPUUs) synthesized with isophorone diisocynate (IPDI) and aliphatic or cycloaliphtic diamines as hard segments are reported. The SMPUUs were proved to be not phase separated while the intermolecular hydrogen bonds gave rise to the physical cross-links. The influences of soft-segment length, hard-segment content (HSC) and type of chain extenders on the structure and properties of the SMPUUs were investigated. As the molecular weight of soft segments (polycaprolactone diols) increased from 4000 to 10 000 g mol-1, shape fixing and shape recoveries of the SMPUUs were raised prominently because the longer polyols favor the crystallization of soft segments in the deformation state and the longer hard segments increase the density of intermolecular hydrogen bonds. The HSC exhibited two opposite effects on shape recovery. Increasing HSC on one hand increased shape recovery due to the increasing stability of physical cross-links and on the other hand reduced shape recovery due to the increasing deformation of hard segments. The polyurethane-urea having isophorone diamines (IPDA) as chain extenders showed over 95% of shape recovery and as high as 4.2 MPa recovery stress. The shape memory properties of the IPDI-based SMPUUs are even comparable with those of aromatic SMPUs.