Optically healable polyurethanes with tunable mechanical properties

The mechanical properties of polyurethanes (PUs), as one of the mostly widely used plastic materials, are usually determined by their constituent components, and are not easily tunable once polymerized. Herein, we report the preparation of a new type of dynamic photo-crosslinkable PUs, by introducing a small content of chain extender-bearing photo-crosslinkable cinnamoyl pendant groups. The mechanical properties of the resultant PUs can be greatly enhanced upon simple UV irradiation. Interestingly, these changes are largely reversible, and the highly crosslinked PUs can be converted back to the thermoplastic state. This interconversion can be repeated several times without significantly impairing the molecular weight and mechanical properties. Taking advantage of the reversible photo-induced crosslinking/decrosslinking process, damaged PUs are fully recoverable via an optical healing process. Lastly, we demonstrated that this simple strategy is extendable to other PU systems, showing the robustness and wide applicability of this approach.