Colorless, transparent, and shape memory polyurethane networks with high strength and recyclability

The traditional thermoset polyurethanes (PUs) can be recycled through the dynamic carbamate bonds under specific conditions. However, there is limited research on the structural evolution and property changes of these PUs before and after recycling. Herein, we designed and fabricated a thermoset polyurethane network (PCU) using polyhexamethylene carbonate diol (PHMC-diol) as soft segments, and isophorone diisocyanate (IPDI) and glycerol (GLY) as hard segments. Through careful formulation design, the PCU demonstrated colorless transparency (with up to 86% transmission), shape memory properties, and reprocessing capabilities, all achieved without introducing other dynamic covalent bonds. Furthermore, the PCU exhibited excellent mechanical properties, boasting a tensile strength of 59.2 +/- 3.7 MPa and the elongation at break of 674.8 +/- 37.3%. Of particular interest, the PCU samples displayed solid-state plasticity and impressive shape memory performance, with shape fixity and recovery ratios exceeding 90%. Leveraging the combination of solid-state plasticity and shape memory, the PCU samples demonstrated the ability to achieve arbitrary shape manipulations. Upon recycling, it was observed that the cross-linking density of the PCU samples decreased, resulting in the formation of byproducts and subsequently leading to a reduction in tensile strength. Nonetheless, the PCU samples prepared in this study exhibit potential as thermadapt shape memory and recyclable materials.