Hexafunctional N/P-Containing Monomer Enabled Epoxy Thermosets With Superior Flame Retardancy and Low Smoke Emission

Epoxy resin (EP) is one of the most widely used thermosetting materials; however, its high inherent flammability severely restricts its practical applications. To address this issue, a novel nitrogen/phosphorus (N/P)-containing hexafunctional monomer (HCPB) was synthesized and employed to partially substitute diglycidyl ether of bisphenol A (DGEBA) in the preparation of flame-retardant epoxy thermosets (EP/HCPB), using polyetheramine (D230) as the curing agent. The effects of HCPB content on the thermal stability, mechanical strength, and flame retardancy of EP were systematically investigated. Specifically, the EP-HCPB 15 composite with 15.00 mol% HCPB achieved a tensile strength of 48.87 MPa, a limiting oxygen index (LOI) of 30.5%, a UL-94 V-0 classification, and a glass transition temperature ( T g ) of 58.11°C. Furthermore, the flame-retardant mechanism of HCPB in the epoxy matrix was systematically elucidated, involving both gas-phase free-radical quenching and condensed-phase charring effects. This work provides a facile and effective strategy for the design and preparation of high-performance flame-retardant epoxy thermosets.