Effect of Silica Fillers on Epoxy–Imidazole Curing Reaction

ABSTRACT (Epoxy–imidazole thermosetting resins exhibit a complex reaction mechanism involving two concurrent processes when heated: exothermic addition polymerization and endothermic reactions, during which the catalyst, imidazole, is regenerated. Thus, the relationship between conversion (defined by enthalpy change) and glass transition temperature varies with curing conditions. Herein, we investigate the effects of fillers on the properties of complex epoxy–imidazole systems. Fast scanning calorimetry reveals that the reaction rate in the samples with filler is delayed. Molecular dynamics simulations show that epoxy groups localize near the OH groups on the filler surface, supporting the interpretation that the addition reaction is suppressed by the formation of epoxy‐imidazole intermediate adducts. Matrix‐assisted laser desorption/ionization–mass spectrometry reveals the formation of short‐length linear chain structures in the early stages of the curing reaction for the filler‐containing sample. This behavior is similar to that observed in the non‐filler system, as reported in a previous study, indicating that the reaction mechanism is preserved in the filler‐containing system. This study provides valuable insights into the epoxy–imidazole reaction mechanism, thereby paving the way for further development of the material and promoting its industrial applications).