Bio-based UV curable polyurethane acrylate: Morphology and shape memory behaviors

Smart bio-based shape memory polymers with high performance and fast response have the exciting potential to meet the growing need in biomedical applications. In this study, novel fast response UV-curable shape memory polyurethane acrylates (SMPUAs) comprising polycaprolactone diols (PCL-Diol), hexamethylene diisocyanate (HDI) and hydroxy-methyl methacrylate (HEMA) were synthesized by two-step bulk polymerization. Two series of PUAs with almost the same amount of hard segment content (HSC) were prepared with varying soft-segment molecular weight (2000, 3000, and 4000 g/mol) and different molar ratios of constituents. A mono-functional reactive diluent was used to control HSC and reduce the viscosity. Morphological characterization revealed nanoscale phase separation in SMPUAs. An increase in soft segment molecular weight was accompanied by an increase in the degree of microphase separation, crystallinity, and stiffness. The results indicated that shape memory behavior of PUAs was affected substantially by soft segment crystallinity and formation of stable ordered hard domains. The versatility of our SMPUAs was further reflected in good shape memory performance (higher than 97% fixity and recovery) with fast response as well as tunable transition temperature.