Covalent Adaptable Networks Containing Nitrogen-Coordinated Boronic Ester and Imine Bonds

Covalent adaptable networks (CANs) are supposed to address the reprocessing and recycling issues of epoxy resins via their reversible cross-linking structures. However, the development of epoxy CANs simultaneously exhibiting high mechanical strength and fast-reprocessing ability is still a huge challenge. Herein, epoxy CANs with high mechanical strength and fast-reprocessing ability are fabricated by modifying linear epoxy polymers with nitrogen-coordinated boronic ester and imine bonds. Owing to their high cross-linking densities and rigid network structures, the obtained epoxy CANs show a high breaking strength of ∼76.0 MPa, a yield stress of ∼81.5 MPa, and Young's modulus of ∼1.67 GPa, respectively. Because of the fast exchange reaction of nitrogen-coordinated boronic ester and imine bonds, the as-prepared epoxy CANs can be easily processed into desirable shapes within only 1 min at 150 °C under a pressure of 10 MPa. Moreover, owing to this unique feature, the epoxy CANs can be quickly reprocessed at least three times without losing their original mechanical properties. Finally, the prepared epoxy CANs exhibit a high shape fixed ratio and a recovery ratio of more than ∼90% when used as shape-memory polymers. This study provides a feasible solution for constructing mechanically strong epoxy thermosets with fast-reprocessing ability, which will contribute to the development of next-generation sustainable epoxy resins.