Highly Thermal Stable, Stiff, and Recyclable Self-Healing Epoxy Based on Diels–Alder Reaction

The low heat resistance of self-healing polymers based on the Diels–Alder (DA) reaction between 2-substituted furans with maleimide has significantly limited their practical applications. To address this limitation, 3-substituted furans instead of 2-substituted furans were used in the reaction with maleimide, which formed a thermally stable conjugated structure in the adduct. As a result, the retro-DA reaction temperature was increased from 120 to 240 °C. Based on such a reaction, a self-healing epoxy resin (SHE) with exceptional heat resistance was successfully synthesized. In addition to its thermal stability, the SHE exhibited a flexural strength and modulus reaching 141.1 MPa and 4.29 GPa, respectively, which were comparable to those of engineering epoxy resins. Moreover, the SHE demonstrated a remarkable self-healing ability and recycling capacity. The healing efficiency of fracture toughness was found to be as high as 85.4%, and the recovery efficiency of flexural strength reached 89.2% after the sample was crushed into powders and recured.