Flexible-Polyester Cross-linked Epoxy Elastomers Based on Dynamic Ester Bonds: High Toughness and Reprocessability

Abstract

Epoxy vitrimers with high cross-linking density and rigid structures were synthesized by reacting of epoxy monomers containing rigid benzene rings with small-molecule curing agents. While the poor toughness (elongation at break ~10%) of epoxy vitrimers limited their applications in the fields of sealing, vibration damping, and impact resistance. In this study, bisphenol A epoxy resin (E44) was employed as the epoxy monomer, and carboxyl-terminated polybutylene adipate (PBA, M_n = 1700–5200) with flexible long chains was used as the curing agent to prepare E44/PBA epoxy elastomers containing dynamic ester bonds. Studies showed that as the molecular weight of PBA increased, the cross-linking density gradually decreased, while the crystallinity progressively increased, thereby influencing the thermal stability, mechanical properties and flexibility of E44/PBA networks. E44/PBA exhibited good thermal stability T_i (306–329°C) and high flexibility ε_b (295.12–553.94%). Among them, E44/PBA₁₇₀₀ demonstrated excellent self-healing, welding, and reprocessability, owing to the highest cross-linking density and abundant β-OH ester bonds, which readily allowed the topological network rearrangement of the epoxy networks. The scratch on E44/PBA₁₇₀₀ could be almost completely healed at 180°C for 30 min. Moreover, the welded E44/PBA₁₇₀₀ exhibited a load-bearing capacity of 200 g after welding at 160°C for 10 min, which was 450 times its own weight. This work supplied a feasible method to prepare epoxy elastomers with high toughness, self-healing, and recyclability.