Overcoming Rigidity Through Flexibility: Epoxy Vitrimer Integrates Ultrahigh Strength, Excellent Network Dynamicity and Closed-Loop Recyclability

Current research on epoxy (EP) vitrimers primarily focuses on enhancing material mechanical properties and self-healing efficiency. However, EPs with high mechanical strength struggle to reconcile network dynamicity due to their high crosslinking density or substantial content of rigid moieties. Consequently, they often require harsh repair/recycling conditions, exhibit low recycling efficiency. In this study, a series of EP vitrimers with different crosslinking network structures was prepared by reacting a high-rigidity group-concentrated multi-reversible dynamic bond long-chain curing agent with a flexible epoxy monomer containing polyether bonds. The concept of crosslinking network rigid-flexible ratio (CRFR) was introduced to quantify the properties. Through structural optimization, the EP vitrimer demonstrated ultrahigh tensile strength (91.6 MPa) and storage modulus (2.65 GPa). Its excellent network dynamicity resulted in an ultra-fast stress relaxation rate (8.7 s at 120°C), outstanding processability and shape-memory properties. Furthermore, the EP vitrimer can be fully degraded at 50°C in either an HCl pure H₂O/DMF solution. The degradation products can be repolymerized directly, enabling green closed-loop recycling with full retention of the original mechanical strength. This work provides an important theoretical foundation and a new pathway for the design of high-strength polymers, as well as for the green recycling of EP vitrimers.