An efficient flame retardant (1,4‐methylenephenylphosphinic acid) piperazine (MPPAP) is successfully synthesized. The application of MPPAP in epoxy (EP) thermosets increases limited oxygen index values of composites to 30.2% and 6 wt% or more loading makes the materials get through UL94 V‐0 rating. The investigation of the combustion process indicates that MPPAP clearly changes the combustion behavior of EP composites, forms a char layer on the surface of the composites, and presents an effective flame inhibition effect, consequently resulting in clear reduction of the flammability and smoke production. The thermal degradation process of MPPAP/EP indicates that MPPAP promotes the matrix to decompose earlier and increases the char‐forming ability of composites. The morphology and structure of the final char shows MPPAP can promote the formation of cross‐linking structures and increase the graphitization degree of char residues acting as an excellent barrier. Furthermore, the flame‐retardant mechanism illuminates that MPPAP can reduce the generation of volatile fuels, and the pyrolysis products of MPPAP contain PO and PO₂, which exert free radical quenching effect in the gas phase. Therefore, MPPAP is a terrific flame retardant for epoxy thermosets which manifests a flame retarding action in the gas phase and condensed phase.

中文翻译：

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（1,4-亚甲基苯基次膦酸）哌嗪的合成及其在环氧树脂热固性塑料中的阻燃性

成功合成了一种高效的阻燃剂（1,4-亚甲基苯基次膦酸）哌嗪（MPPAP）。MPPAP在环氧（EP）热固性塑料中的应用将复合材料的有限氧指数值提高到30.2％，并且负载量达到6 wt％或更高，使材料达到UL94 V-0等级。燃烧过程的研究表明，MPPAP明显改变了EP复合材料的燃烧行为，在复合材料表面形成了一层炭层，并表现出有效的阻火作用，因此导致可燃性和烟雾的产生明显减少。MPPAP / EP的热降解过程表明MPPAP促进了基体更早地分解，并提高了复合材料的成炭能力。最终炭的形态和结构表明，MPPAP可以促进交联结构的形成，并提高炭残渣的石墨化程度，从而起到极好的阻隔作用。此外，阻燃机理表明MPPAP可以减少挥发性燃料的产生，并且MPPAP的热解产物含有PO和PO₂，其在气相中发挥自由基猝灭作用。因此，MPPAP是环氧热固性涂料的绝佳阻燃剂，在气相和冷凝相中均表现出阻燃作用。