A series of novel flame-retardant thermosets were prepared by melt blending of phosphonate–triazine-based compound TNTP, triazine-based compound TN, and phosphonate-based compound TP, respectively. The curing systems were consisted of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diamino-diphenyl sulfone (DDS). The thermal behaviors and flame retardancy of these flame-retardant thermosets were investigated in terms of thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter tests. TGA results showed that the char formation of flame-retardant thermosets could be significantly improved due to the presence of phosphonate moiety rather than triazine unit. It was found that the excellent flame retardant effect of TNTP was not contributed by either single group of phosphonate or triazine. An obvious synergic-effect on flame retardant produced by a combination of phosphonate and triazine moiety. The LOI value of TNTP-3/DGEBA/DDS could achieve 32.4% and reach UL-94 V-0 rating, while that of TN-3/DGEBA/DDS was 29.0% and failed in UL-94 test, and TP-3/DGEBA/DDS with a LOI value of 31.8% just reach UL-94 V-1 rating. Moreover, cone calorimeter test revealed that the incorporation of TNTP to epoxy thermoset with 1.5 wt % phosphorus content could result in a decrease of peak heat release rate (PHRR), total heat release (THR), average mass loss rate (AMLR), total smoke release (TSR), average CO yield (ACOY), and average CO2 yield (ACO2Y) compared with DGEBA/DDS control. The results from TGA data, scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) indicated TNTP modified thermosets had a comprehensive flame retardant mechanism, including the gas phase, condensed phase and phosphorus–nitrogen synergism mechanism. Furthermore, the mechanical properties of all the thermosets were also investigated by Izod impact strength and flexural property tests.

A novel, halogen‐free, phosphorus–nitrogen containing flame retardant 2[4‐(2,4,6‐Tris{4‐[(5,5‐dimethyl‐2‐oxo‐2λ5‐[1,3,2]dioxaphosphinan‐2‐yl)hydroxymethyl]phenoxy}‐(1,3,5)‐triazine (TNTP) was successfully synthesized in a three‐step process, and characterized by FTIR, NMR spectroscopy, mass spectra, and elemental analysis. A series of modified DGEBA epoxy resin with different loadings of TNTP were prepared and cured by 4,4‐diaminodiphenylsulfone (DDS). Thermal gravimetric analysis and vertical burning test (UL‐94) were used to evaluate the flame retardancy of TNTP on DGEBA epoxy resin. The results showed that TNTP had a great impact on flame retardancy. All modified thermosets by using TNTP exhibited higher Tg than pure DGEBA/DDS. The loading of TNTP at only 5.0 wt % could result in satisfied flame retardancy (UL‐94, V‐0) together with high char residue (27.3%) at 700°C. The addition of TNTP could dramatically enhance the flame retardancy of DGEBA epoxy resins, which was further confirmed by the analysis of the char residues by scanning electron microscopy and FTIR. Furthermore, no obviously negative effect was found on the Izod impact strength and flexural property of DGEBA epoxy resins when TNTP loading limited in 5.0 wt %. DGEBA/DDS containing 2.5 wt % TNTP could enhance Izod impact strength from 10.47 to 10.94 kJ m−2, and showed no appreciable effect on the flexural property (85.20 MPa) comparing with pure DGEBA/DDS (87.03 MPa). Results indicated that TNTP as a phosphorus–nitrogen synergistic intumescent flame retardant could be used for DGEBA epoxy resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41079.

A novel nitrogen-containing cyclic phosphate (NDP) was synthesized and well characterized by 1 H, 13 C, 31 P NMR, mass spectra and elemental analysis. NDP was used as an additive intumescent flame retardant (AIFR) to impart flame retardancy and dripping resistance for diglycidyl ether of bisphenol-A epoxy resin (DGEBA) curied by 4,4 0 -diaminodiphenylsulfone (DDS) with different phosphorus content. The flammability, thermal stability, and mechanical properties of NDP modified DGEBA/DDS thermosets were investigated by UL-94 vertical burning test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Izod impact strength and flexural property tests. The results showed that NDP modified DGEBA/DDS thermosets exhibited excellent flame retardancy, moderate changes in glass transition temperature and thermal stability. When the phosphorus content reached only 1.5 wt %, the NDP modified DGEBA/DDS thermoset could result in satisfied flame retardancy (UL-94, V-0). The TGA curves under nitrogen and air atmosphere suggested that NDP had good ability of char formation, and there existed a distinct synergistic effect between phosphorus and nitrogen. The flame retardant mechanism was further realized by studying the structure and morphology of char residues using FT-IR and scanning electron microscopy (SEM). It indicated that NDP as phosphorus-nitrogen containing flame retardant worked by both of the condensed phase action and the vapor phase action. Additionally, the addition of NDP decreased slightly the flexural strength of the flame retarded DGEBA epoxy resins, and increased the Izod impact strength of these thermosets.

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