One Core, Many Cures: Quantitative Design Rules for Ionic Liquid Epoxy Curing Agents

Abstract Epoxy formulations containing a 20-member library of 1-methylimidazolium dicyanamide ionic liquids showed systematic N-substituent-dependent differences in thermal curing behavior. The library comprised alkyl, unsaturated, polar-functionalized, ether/silyl-containing, and aromatic/bulky substituents. Principal component analysis combined five cation descriptors- topological polar surface area, molar refractivity, fraction of sp3-hybridized carbon atoms, number of rotatable bonds, and cLogP - with four differential scanning calorimetry (DSC) parameters (Tp, ΔHc, Tg, ΔTg). Across the library, Tp ranged 120.8–172.5 °C, Tg 46.0–98.6 °C, and ΔHc 141–620 J g–1. PC1 (43.04%) described a polarity–flexibility dimension associated with temperature-related parameters, whereas PC2 (21.85%) was associated primarily with curing enthalpy. PC1 decreased approximately linearly across the C2-C16 alkyl series. Three low-enthalpy systems occupied distinct multivariate regions consistent with possible steric limitation, amide-mediated self-association, or trimethoxysilyl-group reactions. The resulting map provides quantitative within-library design rules under the investigated formulation, fixed molar ionic-pair content, and DSC conditions.