Imidazolium-carboxylate ionic liquids as latent curing agents for epoxy resin with excellent storage, thermal stability, and mechanical properties

Latent curing agents are crucial in one-component epoxy resin formulations; however, the variety of liquid-state ionic liquid latent curing agents remains limited. In this study, a series of novel liquid imidazolium-carboxylate ionic liquids (ICILs) based on 1-methylimidazole (MIM) were developed. These ICILs exhibited excellent miscibility and storage stability with epoxy resin (E-51). At an optimal mass ratio of 5:100, one of the ICILs with CF 3 COO − efficiently cured the epoxy resin at 154 °C and demonstrated a workable pot life that exceeded 27 days. The curing mechanism study by nuclear magnetic resonance (NMR) indicates that the ICILs' anion attacks the epoxy group to initiate ring-opening polymerization. Compared to the MIM/E-51 thermosetting system, the ICILs/E-51 system yields thermosets with superior mechanical property while maintains excellent thermal stability and hydrophobic property. The synthesized ICILs not only serve as potent latent curing agents but also provide valuable insights for the design of next-generation latent curing agents.