Highly Robust and Ultralow Temperature Resistant Epoxy Network Based on Acylhydrazone Bonds: Water Resistant, Shape Memory and Closed-Loop Recyclable

Imine-functionalized epoxy resins have become a research hotspot due to their degradable and recyclable properties. However, the inherent thermodynamic instability of imine bonds poses a challenge in developing multifunctional novel epoxy resins that exhibit high strength and toughness, low-temperature resistance, and environmental stability. In this study, a molecular structure engineering strategy was employed to construct a dual-dynamic supramolecular acylhydrazone-functionalized epoxy network-EPCAN-5. Benefiting from the synergistic cross-linking effect between the reversible hydrogen-bonding network in the gradient-energy structure and the covalent cross-linking network with a rigid-flexible design, this material exhibits ultrahigh strength and toughness (tensile strength of 115 MPa, elongation at break of 12.3%, toughness of 11.01 MJ/m³). It maintains a tensile strength of 140 MPa with 6% elongation even at an extremely low temperature of −50 °C, and retains excellent mechanical stability and flexibility even when immersed in liquid nitrogen (−196 °C). Furthermore, it demonstrates outstanding resistance to water and weak acids, addressing the technical challenge of performance degradation in imine-based epoxy materials under service conditions. The gradient-energy hydrogen-bonding structure endows EPCAN-5 with excellent programmable heat-driven shape memory functionality; a designed hook structure can lift up to 5000 times its own weight and automatically release the load upon reaching the temperature threshold. Additionally, the material can be fully recovered via a catalyst-free closed-loop process, with the repolymerized material retaining 99% of the original mechanical properties. In summary, this work successfully constructed a covalent cross-linking system that integrates gradient hydrogen bonds, reversible covalent bonds, and a balanced combination of rigidity and flexibility. This system exhibits notable advantages, including high strength and toughness, low-temperature resistance, shape memory capability, and environmental stability.