Amide-Functionalized Ionic Liquids As Curing Agents for Epoxy Resin: Preparation, Characterization, and Curing Behaviors with TDE-85

A series of amide-functionalized ionic liquids (ILs), e.g., 1-R-3-(2-amino-2-oxoethyl)-imidazolium (R = −vinyl, −methyl–butyl) cations combined with Cl–, N(CN)2–, or NTf2– anions, were synthesized and fully characterized as curing agent for diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85). Studies of curing behaviors showed that ILs with N(CN)2– anions exhibit moderate curing conditions. As to thermosets of TDE-85 cured by these curing agents, their tensile strength (95.1–111.7 MPa) and elongation at break (2.69 to 4.20%) are significantly improved compared with the traditional curing systems of DDS/TDE-85 (DDS, 4,4′-diamino diphenyl sulphone). These thermosets also exhibit good thermal mechanical properties with the glass transition temperature (Tg) > 200 °C and thermal degradation temperature (Td) > 300 °C. The possible mechanisms of curing reactions were analyzed by using IR, and results indicated that curing reactions of TDE-85 with amide-functionalized ionic liquids may include three steps, −NH2 groups reacted with oxirane at lower temperatures, and then the anions further participated in the reaction to strengthen the cross-linking networks. This study provides informative guidelines for designing new curing agents.