Dual-Functionalized Imidazolium Ionic Liquids as Curing Agents for Epoxy Resins

As epoxy resin curing agents, ionic liquids can help improve mechanical properties, flame retardancy, and wear and tear self-healing and extend the pot life of epoxy compositions. The functional design of ionic-liquid curing agents may significantly improve the overall performance of epoxy resins. In this paper, a series of dual-functionalized ionic liquids, e.g., 1-(3-amino-3-oxopropyl)-3-propynyl-imidazolium, 1-(3-amino-3-oxopropyl)-3-(2-amino-2-oxoethyl)-imidazolium, and 1-allyl-3-(2-amino-2-oxoethyl)-imidazolium combined with dicyanamide (N­(CN)₂^–) or bis­(trifluoromethylsulfonyl)­imide (NTf₂^–) anions, were synthesized and characterized as curing agents for diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85). The results showed that the obtained bifunctional ionic liquids can be used as a medium or high-temperature curing agents for TDE-85 with the curing temperature range of 130–208 °C and the best mass ratio range of 15:100–40:100. Thermosets obtained from the bifunctional ionic liquid and TDE-85 curing system exhibit better heat resistance with the glass transition temperature of 187–212 °C and the decomposition temperature at 10% weight loss of 282–357 °C. The curing reaction mechanism of the 1-(3-amino-3-oxopropyl)-3-(2-amino-2-oxoethyl)-imidazolium NTf₂^–/TDE-85 system mainly has three processes.