A degradable and tough supramolecular epoxy network with shape memory and clustering-triggered emission functions

Abstract

Epoxy resins with covalent bond cross-linked networks have high strength and are widely used in many fields, but how to endow epoxy resins with recyclability and multifunctionality while achieving balanced integration of high strength and toughness will be a significant challenge. In this work, through molecular engineering, a VA hardener with a hydrogen-bonding site and a VM hardener without a hydrogen-bonding site were synthesized by the reaction of 4-imidazolecarboxaldehyde with two diamines, respectively. The two hardeners were mixed according to a certain ratio and then reacted with flexible epoxy monomers, and a new supramolecular epoxy network composed of dynamic covalent bonds (imine bonds) and adjustable dynamic noncovalent bonds (hydrogen bonds and metal-coordination bonds) was built by the addition of Zn²⁺. This unique dynamic network achieves a strength-toughness trade-off, including a tensile strength of 54 MPa, an elongation at break of 22.3%, and a toughness of 8.96 MJ m⁻³, with a shape-memory function triggered by temperature. Surprisingly, all specimens exhibit clustering-triggered emission (CTE), displaying fluorescence under ultraviolet (UV) light, with the mechanism being illustrated using density functional theory (DFT). Finally, the integration of dynamic imine bonds enables closed-loop recycling and reprocessing of the specimen. This study develops a multifunctional supramolecular epoxy system that harmonizes mechanical robustness, stimuli-responsiveness (shape memory/fluorescence), and circular lifecycle capabilities, contributing to the advancement of sustainable polymer design paradigms.