Dynamic Curing Agents for Amine-Hardened Epoxy Vitrimers with Short (Re)processing Times

This work presents a straightforward strategy to introduce highly dynamic and adaptable cross-links into common epoxy resin formulations. For this, an oligomeric amine-based curing agent containing vinylogous urethane (VU) bonds was developed. This novel polyfunctional amine curing agent can be used as a drop-in solution for existing epoxy resin technologies, resulting in transparent, rigid, and, at the same time, highly reprocessable catalyst-free epoxy vitrimers. The oligomeric VU-curing agents are prepolymerized via a straightforward condensation reaction between acetoacetates extended with different classical amine monomers and epoxy hardeners. It is found that vitrimer properties can be readily introduced into these epoxy formulations by converting <50 mol % of the hardener's amine functionalities into dynamic vinylogous urethane bonds. In this way, epoxy vitrimers can be obtained with material properties comparable to ones of the VU-free epoxy formulations. In addition, remarkably short processing times are observed in the absence of any catalyst, and the material displayed very short stress relaxation times and good recyclability, actually representing the most performant VU-based vitrimers so far. Furthermore, a proof of concept for its use in obtaining glass-fiber-reinforced epoxy composites is also presented.