A novel epoxy resin system containing bismaleimide and DOPO-based flame retardant with excellent flame retardancy and toughness

9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide (DOPO) and special tetra functional epoxy resin (EP) AG-601 were combined to synthesize a reactive flame retardant (FREP) and then incorporated into EP, obtaining the flame retardant material EP/FREP. To achieve EPs with higher flame retardancy and mechanical properties, a new intrinsically flame retardant EP system named EP/FRDM was produced by modifying EP/FREP with high thermal resistance bismaleimide (BDM). In the presence of a distinct FRDM structure comprising phosphaphenanthrene/nitrogen, the EP possessed superior flame retardancy and impact toughness. The curing process of EP/FRDM was investigated using Real-Time Fourier-transform Infrared. In terms of fire performance, the limiting oxygen index of the EP/FRDM-3 was raised from 31.4% to 38.2%, and the vertical burning rating was improved after BDM was added to the EP/FREP system. It was discovered that EP/FRDM exhibited a classic two-phase flame retardant influence by analyzing the residual carbon morphology and pyrolysis behavior. Simultaneously, the glass transition temperature (T-g) of EP/FRDM remained essentially stable, and the char residue yield rose markedly, which indicated that the system had outstanding thermal stability, according to the results of the dynamic mechanical analysis and thermogravimetric analysis tests. Notably, the EP/FRDM experienced an internal chain expansion reaction when BDM was added, giving flame retardant materials excellent flexural and impact strengths and promising future application opportunities.