Dual-Functionalized Imidazolium Ionic Liquids as Curing Agents for Epoxy Resins
Zhiyi Jiang, Qingchen Wang, Long Liu, Yanqiang Zhang, Fang Du, Aimin Pang
Abstract
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.