反应型磷杂菲多氮杂环双基苯并噁嗪高效提升环氧树脂阻燃性能和玻璃化温度研究

Epoxy resin shows great application potential in the fields requiring flame resistance such as aerospace, electrical and electronic industries. Unfortunately, its flammable nature and poor heat resistance have severely restricted its further applications. As novel flame retardants for epoxy resin, DOPO and its derivatives have attracted great attention from both industrial and academic research studies. However, their flame-retardant efficiency should be further improved. Moreover, their incorporation may result in the sharp decrease of glass transition temperature (Tg) of epoxy resin. In this project, in view of the synergistic flame-retardant effect between phosphaphenanthrene and multi-nitrogen heterocycle, along with the ring-opening nature of benzoxazine unit when exposed to heat, a series of novel and reactive benzoxazines containing phosphaphenanthrene and multi-nitrogen heterocycle groups (DOPO-BZ) will be synthesized. As co-curing agents, they could be incorporated into epoxy matrices to prepare epoxy thermosets with superior flame retardancy and high Tg. The curing behavior of flame-retardant epoxy system will be investigated to gain insight into the curing mechanism and process. The influence of DOPO-BZ on the thermal, mechanical and flame-retardant properties of epoxy thermosets will be studied to establish the relationship between the chemical structure of DOPO-BZ and properties of flame-retardant epoxy resin. In addition, the flame-retardant mechanism of DOPO-BZ can be elucidated by analyzing the gaseous pyrolytic products, along with investigating the structure and chemical composition of char residues generated after pyrolysis or combustion process of flame-retardant epoxy thermoset. The result of this project will provide new ideas for developing highly efficient flame retardant and flame-retardant epoxy resin with high Tg. Moreover, it will lay the theoretical and experimental foundation for broadening the application of epoxy resin in the fields requiring flame resistance such as aerospace, electrical and electronic industries.

易燃及耐热性差是制约环氧树脂在电子电气、航空航天等领域应用的主要瓶颈。当前，DOPO及其衍生物已成为阻燃环氧树脂的研究热点，但普遍存在阻燃效率偏低和阻燃树脂的玻璃化温度（Tg）降低明显等不足。考虑到多氮杂环和磷杂菲基团间的协同阻燃效应以及苯并噁嗪单元的受热开环交联特性，本项目拟合成反应型磷杂菲多氮杂环双基苯并噁嗪（DOPO-BZ），将其以共固化剂引至环氧体系，制备兼具优异阻燃性能和高Tg的环氧树脂。研究阻燃环氧体系的固化行为，明确其固化机理和工艺；考察DOPO-BZ对环氧固化物热性能、力学性能和阻燃性能的影响，建立其分子结构与阻燃固化物性能间的关系；通过对阻燃固化物的热裂解气相产物，以及在热降解或燃烧后生成炭层的结构和化学组成进行研究，阐明DOPO-BZ的阻燃机理。项目研究成果可为研发新型高效阻燃剂和高Tg的阻燃环氧树脂提供较好研究思路，并为拓展环氧树脂的应用领域奠定一定的理论和实验基础。

项目针对DOPO衍生物阻燃效率偏低和阻燃环氧固化物玻璃化温度、力学性能下降明显的难题，设计合成了含杂原子的反应型磷杂菲磺胺胍低聚物、磷杂菲磺胺噻唑化合物、磷杂菲多氮杂环低聚物，将其作为共固化剂引至环氧体系，制备了耐热性好、阻燃性能优异、力学性能优良的环氧固化物。研究了阻燃环氧体系的固化行为，考察了阻燃剂对环氧固化物热性能、力学性能和阻燃性能的影响，探究了阻燃环氧固化物的阻燃机理。研究表明：阻燃剂能够与环氧树脂发生化学反应，显著降低环氧体系的反应活化能，促进环氧体系的交联固化反应。阻燃剂与环氧树脂的额外化学交联以及刚性基团的空间位阻有助于极大程度地保留环氧固化物的玻璃化温度。阻燃剂分子结构中的苯环及杂原子（N，S）可与环氧大分子链形成π-π相互作用力和氢键，提升阻燃环氧固化物的力学性能。阻燃基团间的协同效应赋予阻燃剂出色的阻燃效率，仅需约0.5 wt%的磷含量即可使得环氧固化物通过UL-94 V-0级测试。阻燃剂均可在气相和凝聚相发挥阻燃作用，在气相稀释可燃物和氧气、猝灭自由基，在凝聚相促进环氧基材成炭。在本项目的执行过程中，以唯一通讯作者发表SCI收录论文6篇，EI收录论文1篇，申请1项国家发明专利。项目成果为今后研发新型高效阻燃剂和耐热性好、阻燃性能优异、力学性能优良的环氧树脂提供较好的研究思路。