A DOPO‐based reactive flame retardant containing benzimidazole groups: Synthesis and its flame‐retardation on epoxy resin

Abstract DOPO based flame retardants demonstrate exceptional flame retardancy efficiency when applied to epoxy resins. However, the crosslinking degree of epoxy resin may decrease due to the addition of DOPO, leading to a deterioration in flame retardancy and mechanical properties. Herein, a reactive DOPO derivative flame retardant 6‐((1H‐benzo[d]imidazol‐2‐yl) amino) dibenzo oxaphosphinine 6‐oxide (BADO) was successfully synthesized, which contains multiple reactive sites, thus ensuring a higher degree of crosslinking in the system. As a result, the modified epoxy resin exhibits excellent flame retardancy. The limiting oxygen index value of the modified epoxy resins increased from 19.8% to 29.7% by adding 7.5 wt% BADO, and its UL‐94 test passed V‐0. Flame retardancy mechanism analysis reveals that BADO exhibits both gas‐phase and condensed‐phase flame retardant effects. In particular, the formation of a porous inside‐char layer is a significant factor in reducing smoke release. The 7.5% BADO/EP composite exhibited a 43.2% reduction in total smoke production and a 43.6% reduction in total smoke rate compared to neat epoxy resins (EP). Furthermore, the addition of BADO slightly deteriorates the mechanical properties of the modified epoxy resin.