Poly(dl-Lactic Acid)-Based Linear Polyurethanes Capable of Forming Physical Crosslinking via UPy Quadruple Hydrogen Bonding Assembly

Linear shape memory polyurethanes based on poly( dl -lactic acid) (PDLLA) macrodiol (PDLLA-SMPUs) have various advantages such as good processability, biodegradability, shape memory effect, and biocompatibility, yet the insufficient mechanical properties prevent their effective applications in bone repair. 2-Ureido-4[1 H ]-pyrimidone (UPy) can form strong quadruple hydrogen bonding. Here, a new linear PDLLA-SMPU containing pendant UPy units (UPy- p -PDLLA-SMPU) is designed and synthesized. The pendant UPy units may dimerize to form physical crosslinking among UPy- p -PDLLA-SMPU chains. As a result, UPy- p -PDLLA-SMPU demonstrates both good processability and significantly higher mechanical properties than the corresponding linear PDLLA-SMPU without pendant UPys. In addition, UPy- p -PDLLA-SMPU shows excellent shape memory effect near body temperature, with a shape fixity ratio of up to 98.6% and a recovery ratio of up to 92.9%. This work provides a new strategy to design SMPUs integrating the merits of linear and crosslinked polyurethanes, and the obtained UPy- p -PDLLA-SMPU is a promising material for bone tissue repair in view of the mechanical, thermal, and shape memory properties.