Nonconventional phosphorus-based tertiary amine curing agent enabling the high fire safety, outstanding tensile strength and high glass transition temperature of epoxy resin

•Nonconventional P-containing tertiary amine curing agent was developed.•P-based tertiary amine cured epoxy resins possessed tensile strength up to 97.4 MPa.•P-based tertiary amine cured epoxy resins displayed Tg up to 171 °C.•P-based tertiary amine cured epoxy resins showed low fire hazard. Epoxy resins (EP) bearing the functionalities of high glass transition temperature (Tg), fire safety, and strong mechanical properties are highly desired, yet the preparation still remains challenging due to the obstacle in realizing the unification of structure rigidity, flame-retardant efficiency, and intermolecular forces. Herein, a new phosphorus-containing tertiary amine, designated as DPDA, is developed as a curing agent for the preparation of desirable epoxy thermosets. The resultant EP-DPDA can self-extinguish quickly during tests, affording a V-0 rating as well as the LOI value of 29.2 %. Cone calorimeter tests (CCT) demonstrate that EP-DPDA performs significantly lower heat release and smoke/toxic gases production, especially for peak of heat release rate (PHRR), smoke production rate (SPR), and CO2 production (CO2P), which show decrease by 76.5 %, 56.4 %, and 79.8 %, respectively, compared to 2-dimethylaminoethylamine (DMEDA) cured EP. The superior flame retardancy is contributed to the roles of trapping radicals and catalyzing effect on the char formation of DPDA fragment. In addition, EP-DPDA exhibits a higher Tg (171 °C) and superior mechanical properties, including an outstanding tensile strength up to 97.4 MPa with a 36.8 % increase as compared to EP-DMEDA, which is related to the existence of rigid cyclic structures and the enhanced intermolecular forces. Generally, this study provides an approach to develop a nonconventional tertiary amine-based flame retardant hardener with promising application in high-performance EP.