In this work, two kinds of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based phosphonamidate flame retardants named 4,4′-diamino-diphenyl methane (DDM)-DOPO and morpholine (MPL)-DOPO are successfully synthesized by the classic Atherton–Todd reaction, and their chemical structures are characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Epoxy composites containing DDM-DOPO or MPL-DOPO are prepared, which still retain relatively high transparency compared with pure epoxy resin (EP). Its fire behavior is studied in terms of vertical burning test (UL-94), limiting oxygen index (LOI), and cone calorimeter tests. The LOI values can achieve 30% and UL-94 test past V-0 rating for DDM-DOPO-modified epoxy composites with 0.25 wt% phosphorus content. The cone calorimeter results indicate that the modified epoxy composites can release less heat and smoke compared with pure EP. Also, thermal degradation behavior and flame-retardant mechanism of epoxy composites are investigated by thermogravimetric analysis and thermogravimetric analysis/infrared spectrometry. The results indicate that two DOPO-based phosphonamidates show a significant gaseous-phase effect on reducing the release of combustible volatiles.
WuCSLiuYLChiuYS. Epoxy resins possessing flame retardant elements from silicon incorporated epoxy compounds cured with phosphorus or nitrogen containing curing agents. Polymer2002; 43: 4277–4284.
2.
LiuHXuKAiH. Preparation and characterization of phosphorus-containing Mannich-type bases as curing agents for epoxy resin. Polym Adv Technol2009; 20: 753–758.
KandolaBKHorrocksARMylerP. New developments in flame retardancy of glass-reinforced epoxy composites. J Appl Polym Sci2003; 88: 2511–2521.
5.
HeSJShiKYGuoXZ. Properties of methyltetrahydrophthalic anhydride-cured epoxy resin modified with MITU. Polym Adv Technol2009; 20: 130–134.
6.
RakotomalalaMWagnerSDöringM. Recent developments in halogen free flame retardants for epoxy resins for electrical and electronic applications. Materials2010; 3: 4300–4327.
7.
ZhangWLiXYangR. Blowing-out effect and temperature profile in condensed phase in flame retarding epoxy resins by phosphorus-containing oligomeric silsesquioxane. Polym Adv Technol2013, 24: 951–961.
8.
ZangLWagnerSCiesielskiM. Novel star-shaped and hyperbranched phosphorus-containing flame retardants in epoxy resins. Polym Adv Technol2011; 22: 1182–1191.
9.
IjiMKiuchiYSoyamaM. Flame retardancy and heat resistance of phenol-biphenylene-type epoxy resin compound modified with benzoguanamine. Polym Adv Technol2003; 14: 638–644.
10.
WangXHuYSongL. Flame retardancy and thermal degradation mechanism of epoxy resin composites based on a DOPO substituted organophosphorus oligomer. Polymer2010; 51: 2435–2445.
11.
WangXHuYSongL. Thermal degradation mechanism of flame retarded epoxy resins with a DOPO-substitued organophosphorus oligomer by TG-FTIR and DP-MS. J Anal Appl Pyrolysis2011; 92: 164–170.
12.
WangYYuanYZhaoY. Flame-retarded epoxy resin with high glass transition temperature cured by DOPO-containing H-benzimidazole. High Perform Polym2017; 29: 94–103.
13.
QianXSongLJiangS. Novel flame retardants containing 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and unsaturated bonds: synthesis, characterization, and application in the flame retardancy of epoxy acrylates. Ind Eng Chem Res2013; 52: 7307–7315.
GuLChenGYaoY. Two novel phosphorus–nitrogen-containing halogen-free flame retardants of high performance for epoxy resin. Polym Degrad Stab2014; 108: 68–75.
16.
QianLQiuYLiuJ. The flame retardant group-synergistic-effect of a phosphaphenanthrene and triazine double-group compound in epoxy resin. J Appl Polym Sci2014; 131: 3.
17.
YangSWangJHuoS. The synergistic effect of maleimide and phosphaphenanthrene groups on a reactive flame-retarded epoxy resin system. Polym Degrad Stab2015; 115: 63–69.
18.
YuanYYangHYuB. Phosphorus and nitrogen-containing polyols: synergistic effect on the thermal property and flame retardancy of rigid polyurethane foam composites. Ind Eng Chem Res2016; 55: 10813–10822.
19.
QinYXuGWangY. Preparation of phosphorus-containing epoxy emulsion and flame retardancy of its thermoset. High Perform Polym2014; 26: 526–531.
20.
JianRWangPDuanW. Synthesis of a novel P/N/S-containing flame retardant and its application in epoxy resin: thermal property, flame retardance, and pyrolysis behavior. Ind Eng Chem Res2016; 55: 11520–11527.
21.
JiangPGuXZhangS. Synthesis, characterization, and utilization of a novel phosphorus/nitrogen-containing flame retardant. Ind Eng Chem Res2015; 54: 2974–2982.
22.
YangSWangJHuoS. Preparation and flame retardancy of an intumescent flame-retardant epoxy resin system constructed by multiple flame-retardant compositions containing phosphorus and nitrogen heterocycle. Polym Degrad Stab2015; 119: 251–259.
23.
QianLJYeLJXuGZ. The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups. Polym Degrad Stab2011; 96: 1118–1124.
24.
YangSWangJHuoS. Synthesis of a phosphorus/nitrogen-containing additive with multifunctional groups and its flame-retardant effect in epoxy resin. Ind Eng Chem Res2015; 54: 7777–7786.
25.
SunDYaoY. Synthesis of three novel phosphorus-containing flame retardants and their application in epoxy resins. Polym Degrad Stab2011; 96: 1720–1724.
26.
XiongYQZhangXYLiuJ. Synthesis of novel phosphorus-containing epoxy hardeners and thermal stability and flame-retardant properties of cured products. J Mater Chem A2012, 125: 1219–1225.
27.
WangTWangJHuoS. Preparation and flame retardancy of DOPO–based epoxy resin containing bismaleimide. High Perform Polym2016; 28: 1090–1095.
28.
GuLQiuJSakaiE. A novel DOPO-containing flame retardant for epoxy resin: synthesis, nonflammability, and an optimized curing procedure for high performance. High Perform Polym2017; 29: 899–912.
29.
YouGChengZTangY. Functional group effect on char formation, flame retardancy and mechanical properties of phosphonate-triazine-based compound as flame retardant in epoxy resin. Ind Eng Chem Res2015; 54: 7309–7319.
30.
WangXHuYSongL. Synthesis and characterization of a DOPO-substitued organophosphorus oligomer and its application in flame retardant epoxy resins. Prog Org Coat2011; 71: 72–82.
31.
Le CorreSSBerchelMCouthon-GourvèsH. Atherton-Todd reaction: mechanism, scope and applications. Beilstein J Org Chem2014; 10: 1166.
32.
NeisiusNMLutzMRentschD. Synthesis of DOPO-based phosphonamidates and their thermal properties. Ind Eng Chem Res2014; 53: 2889–2896.
33.
FengXXingWSongL. In situ synthesis of a MoS2/CoOOH hybrid by a facile wet chemical method and the catalytic oxidation of CO in epoxy resin during decomposition. J Mater Chem A2014; 2: 13299s–13308.
34.
TaoLZhaoGBQianJ. TG-FTIR characterization of pyrolysis of waste mixtures of paint and tar slag. J Hazard Mater2010; 175: 754–761.
