A multifunctional P/Si-containing imidazole curing agent toward advanced one-component epoxy resins with superior flame retardancy and mechanical properties

To simplify the preparation process of epoxy resin (EP) products and overcome their flammability, there is a growing demand for the development of high-performance single-component flame-retardant EP systems. However, existing strategies face challenges in simultaneously achieving flame retardancy and mechanical properties. Herein, a phosphorus/silicon-derived, imidazole-based oligomer (DM) was synthesized and applied as a latent curing agent for EP. DM exhibits great storage stability and fast curing rate. Thanks to the synergistic flame retardant effect of P- and Si-containing groups in the gas and condensed phases, the EP cured by 36 wt% DM (EP/DM-36) features excellent flame retardancy, with a limiting oxygen index (LOI) of 32.0 % and a vertical burning (UL-94) V-0 rating, and its peak heat release rate (PHRR) and total heat release rate (THR) are reduced by 57.1 % and 45.4 % relative to those of the EP cured by 6 wt% imidazole (EP/IM-6). The flexible Si O bonds and oligomer structure of DM endow EP/DM-36 with outstanding mechanical properties, as reflected by 49.4 %, 37.0 %, 108.7 %, and 89.0 % enhancements in tensile strength, elongation at break, impact strength, and toughness compared with those of EP/IM-6. Therefore, the excellent flame retardancy and mechanical properties of EP/DM-36 make it superior to previously reported one-component flame-retardant EPs. This work presents a viable design strategy for developing one-component epoxy systems with exceptional flame retardancy, mechanical properties, and storage stability. • A P/Si/imidazole-based oligomer (DM) was synthesized as a latent curing agent for EP. • DM exhibits great thermal latency and fast curing rate. • EP cured by 36 wt% DM (EP/DM-36) features excellent flame retardancy. • DM endows EP/DM-36 with outstanding mechanical properties.