A multifunctional P/Si-containing imidazole curing agent toward advanced one-component epoxy resins with superior flame retardancy and mechanical properties
Cheng Wang, Haonan Wang, Guofeng Ye, Yong Guo, Qingshan Yang, Asim Mushtaq, Min Hee Hong, Tielin Wang, Siqi Huo
Abstract
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.