Synergistic engineering of phosphaphenanthrene and ionic liquids for unlocking flame retardant multifunctional epoxy resin with high performances

Herein, we presented a multifunctional epoxy resin (EP) composite prepared by the synergistic combination of DOPO and ionic liquids (ILs). The optimized EP-DOPO/ILs system demonstrated exceptional flame retardancy, with only 3 wt% of flame retardant (DOPO/ILs) added to achieve UL-94 V-0 grade for EP and a limiting oxygen index (LOI) of 33.4%. Cone calorimeter test revealed 32.2% and 26.7% reductions in peak of heat release rate (pHRR) and total smoke production (TSP), respectively, compared to neat EP. Notably, the designed rigid-flexible epoxy network simultaneously enhanced tensile strength to 75.7 MPa (+15.7%) and impact strength to 24.8 kJ m -2 (+136.3%), outperforming conventional EP thermosets. Furthermore, the EP composites retained 90% visible light transmittance while exhibiting ultraviolet (UV) shielding efficiency and intrinsic fluorescence. This multi-component collaborative system provides an important experimental foundation for developing high-performance multifunctional polymeric materials.