In order to attain highly efficient flame retardant epoxy thermosets without deteriorating the thermo-mechanical performances, a 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)-derived compound (tetra-DOPO) with different oxidation states of phosphorus and rich aromatic structures was successfully synthesized via addition and Atherton–Todd reactions. The molecular structure of tetra-DOPO was confirmed by the FTIR, ¹H- and ³¹P-NMR spectra. The DMA measurement indicated that the addition of 5.0 wt% of Tetra-DOPO enhanced both the storage modulus and the glass transition temperature of the epoxy composite. The EP composite containing 5.0 wt% of Tetra-DOPO had an LOI of 30.0% and UL-94 V-0 grade, indicating the exceptional fire-retardant efficacy of tetra-DOPO. Additionally, in the cone calorimeter test, the PHRR, THR, and TSP values of EP/tetra-DOPO-5.0 were declined by 25.1%, 18.7%, and 13.9%, respectively, as compared to those of the EP. The reduced mean EHC value suggested the flame inhibition mechanism of tetra-DOPO in the vapor phase by emitting PO• radicals to quench the combustion chain reaction. The flame retardant mechanism of Tetra-DOPO was further clarified by detecting the pyrolytic gas species using TGA-FTIR as well as analyzing the microstructure of the char residues using SEM and Raman spectrometer. The main flame retardant mode of action of Tetra-DOPO was flame inhibition in the vapor phase, while it also played a relatively minor role in the condensed phase by forming an intact and compact char layer containing high graphitized structure.

为了在不降低热机械性能的情况下获得高效的阻燃环氧树脂热固性材料，一种具有不同氧化态的 9,10-二氢-9-氧杂-10-磷杂菲 10-氧化物 (DOPO) 衍生化合物 (四-DOPO)通过加成和 Atherton-Todd 反应成功合成了磷和丰富的芳香结构。四-DOPO的分子结构经FTIR、¹ H-和³¹P-核磁共振谱。DMA 测量表明，添加 5.0 wt% 的 Tetra-DOPO 提高了环氧树脂复合材料的储能模量和玻璃化转变温度。含有 5.0 wt% Tetra-DOPO 的 EP 复合材料具有 30.0% 的 LOI 和 UL-94 V-0 等级，表明四-DOPO 具有卓越的阻燃功效。此外，在锥形量热仪测试中，与 EP 相比，EP/tetra-DOPO-5.0 的 PHRR、THR 和 TSP 值分别下降了 25.1%、18.7% 和 13.9%。降低的平均 EHC 值表明 tetra-DOPO 在气相中的火焰抑制机制是通过释放 PO• 自由基来淬灭燃烧链反应。通过使用 TGA-FTIR 检测热解气体种类以及使用 SEM 和拉曼光谱仪分析炭残留物的微观结构，进一步阐明了 Tetra-DOPO 的阻燃机制。Tetra-DOPO 的主要阻燃作用方式是气相中的阻燃作用，而它在凝聚相中也起到了相对次要的作用，形成了完整且致密的炭层，含有高石墨化结构。