A flame-retardant tris (3-nitrophenyl) phosphine (NPPh3) containing nitro group was synthesized from triphenyl phosphine (PPh3). Its chemical structure, thermal stability, thermal degradation behavior, charring ability, and thermal degradation products were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (1HNMR), thermogravimetric analysis (TG), and thermogravimetric analysis/infrared spectrometry(TG-FTIR). The results showed that the initial thermal decomposition temperature of NPPh3 was 291.2 ℃. The carbon residue at 800 ℃ (under N2atmosphere) reached 28.16 %, which demonstrated that the thermal stability and charring ability of PPh3 after nitrification was improved. In addition, TG-FTIR results indicated that its thermal degradation products were H2O, CO2, CO, and aromatic ring. In order to achieve a good flame retardant effect under less flame retardant, NPPh3 was used together with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to prepare a flame-retardant system for epoxy resins(EP) with 4,4-diaminodiphenylmethane (DDM) as curing agent, and the synergistic effect between them was studied.LOIand UL-94 results showed that when the flame retardant content was 4.7 %, the ratio of NPPh3/DOPO was at 1:2, flame retardant epoxy resin acquired aLOIvalue of 33.8 % and UL-94 vertical burning successfully passed V-0 flammability rating. The TG test showed that there was an obvious synergistic effect between NPPh3 and DOPO. The introduction of NPPh3/DOPO lowered the initial decomposition temperature and increased the amount of residue mass at high temperature compared with EP. Additionally, the structure and morphology of the residue chars were studied by FTIR and scanning electron microscopy(SEM). The results illustrated that NPPh3/DOPO stimulated the formation of compact and strong char layer which contained -P and -NO2groups, and provided a good barrier to hamper the transfer of heat and oxygen into the combustion layer. Consequently, the underlying epoxy resins were protected from further degradation and combustion, and led to an efficient flame retardant in condensed phase.
