Thermal latent curing agent for epoxy resins from neutralization of 2‐methylimidazole with a phosphazene‐containing polyfunctional carboxylic acid

Abstract

A novel thermal latent curing agent, 2MZS, was obtained through the reaction of 2‐methylimidazole (2MZ) and a symmetrically carboxyl‐functionalized star‐shaped molecule based on cyclotriphosphazene (N3P3‐COOH). In the complex, the resonance of N3P3‐COOH reduced the activity of lone electron pairs on the pyridine‐type nitrogen atom of imidazole ring, suppressing the nucleophilic attack and crosslinking reaction between 2MZ and epoxy resin. As a result, the storage stability was improved distinctly for the one‐pot epoxy compound, which could be steadily stored at room temperature for nearly 1 month. Nonisothermal DSC revealed a delayed initiation curing mechanism of the prepared one‐pot system, and which could undergo rapid curing reaction upon raising the temperature. Moreover, the introduction of terminally polyfunctional star‐shaped phosphazene derivative could promote the curing process at elevated temperature, as well as improve the chain rigidity of the cured resin by chemical incorporation into the cross‐linked network, thus endowing the cured resin with enhanced glassy storage modulus. The epoxy thermoset exhibited the highest glass transition temperature and thermal degradation temperature when 20 wt% of 2MZS was used. It is suggested that the novel latent curing agent is potential for high‐performance one‐pot epoxy compound, particularly recommended for application in electronic packaging fields.