A phosphorus-containing tertiary amine hardener enabled flame retardant, heat resistant and mechanically strong yet tough epoxy resins

Although current phosphorus (P)-based hardeners endowed epoxy resins (EPs) with intrinsic flame retardancy, their addition usually reduced thermal and mechanical properties. In this work, a novel phosphorus-containing tertiary amine hardener (DCM) was synthesized using diphenylphosphinic chloride and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and applied to fabricate high-performance EP/DCM. Introducing P-containing group reduced the reactivity of tertiary amine of DCM, but EP/DCM gelled at 100 °C within 11.3 min, showing modest-temperature curing character. EP/DCM exhibited higher glass-transition temperature (Tg) and char yield than virgin EP/DMP-30. Moreover, EP/DCM featured superior mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 61.2%, 72.0% and 198.5%, respectively, relative to those of EP/DMP-30. DCM endowed EP thermosets with remarkable flame retardancy and smoke suppression. The limiting oxygen index (LOI) and UL-94 rating of EP/DCM reached 35.7% and V-0, respectively, with 36.2% and 22.6% reductions in peak heat release rate (PHRR) and peak smoke production rate (PSPR) compared with those of EP/DMP-30. This work pioneers an innovative strategy for creating high-performance EPs with satisfactory heat resistance, fire safety, and mechanical properties by curing with P-containing tertiary amine hardeners.