Preparation of a Novel Phosphorus–Nitrogen‐Containing Flame Retardant by Supramolecular Reaction and its Application in Epoxy Resin

Piperazine hexahydrate (PI) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) are used to synthesize flame‐retardant PI‐DTPMP through supramolecular reaction. The incorporation of PI‐DTPMP simultaneously improves the mechanical and flame‐retardant properties of epoxy resin (EP). With only 5 wt% loading of PI‐DTPMP, EP composites show excellent flame retardancy with a limiting oxygen index (LOI) of 36.4% and V‐0 rating in the UL‐94 test. The cone calorimetric test results demonstrates that the peak heat release rate, total heat release, and total smoke release of EP/5%PI‐DTPMP are reduced by 44.9%, 34.7%, and 37.7% compared with that of neat EP, respectively, owing to the formation of compact and insulating char layer during combustion. Moreover, EP/PI‐DTPMP composites show enhanced mechanical properties with the improved tensile and impact strength, as well as higher storage modulus, crosslink densities, and glass‐transition temperatures in dynamic mechanical analysis.