Preparation of renewable gallic acid-based self-healing waterborne polyurethane with dynamic phenol–carbamate network: toward superior mechanical properties and shape memory function

Endowing thermoset self-healing polymers with excellent mechanical properties and shape memory function by utilizing bio-based monomers is highly desirable for the development of the next-generation smart materials. To achieve this goal, herein, we developed a novel thermally induced self-healing system with robust mechanical properties and shape memory function by incorporating dynamic phenol–carbamate bond formed by the polymerization reaction of the renewable gallic acid (GA) and isocyanate into waterborne polyurethane (GA-WPU) with excellent emulsion stability. The mechanical properties and thermal stability of the resulting polymers were much improved due to the introduction of phenol–carbamate networks. Moreover, the crystallization and microphase separation were evaluated to deeply insight into the effect of GA moieties incorporated into the polymer chains of GA-WPU. Significantly, a good balance can be achieved between desirable self-healing ability (healing efficiency 81.1%) and robust mechanical properties (tensile strength 45.1 MPa and elongation at break 576.5%) by adjusting dynamic phenol–carbamate bonds incorporated into the polymer networks, and compared with the reported self-healing polymers, the recovered tensile strength of our target polymer shows an overwhelming superiority. Furthermore, taking the advantage of the crystalline PBA (switching segment) and phenol–carbamate cross-linkages, the prepared GA-WPU polymer can rapidly recover from temporary shape to original shape by thermal energy (less than 30 s, and the shape fixity and recovery ratio remain above 91.5%). We envision that this elaborate strategy is instructive for designing mechanically robust polymeric materials with self-healing, shape memory function and environmentally friendly characteristics.Graphical abstract