含碳硼烷单元聚酰亚胺材料的制备及其耐热机制

聚酰亚胺是先进复合材料重要的基体材料之一。在聚酰亚胺主链中成功引入碳硼烷笼状单元，制备出一系列有机-无机杂化的聚酰亚胺材料。从单体设计入手，设计合成了含邻碳硼烷单元的二胺单体(DNCB)，再与4,4’-二氨基二苯醚(ODA)和3,3’,4,4’-苯甲酮四羧酸二酐(BTDA)进行共聚反应，合成前驱体聚酰胺酸(PAA)溶液并制备PAA薄膜，再经高温热亚胺化处理得到含碳硼烷单元的聚酰亚胺。对制备的聚酰亚胺材料的耐热性能和耐热氧化稳定性进行了系统研究，结果表明，碳硼烷单元的引入使聚酰亚胺基体的热稳定性和热氧化稳定性得到显著提升。当二胺单体中DNCB摩尔分数为40%时，N₂气氛下，5wt%热失重温度T_5%提升近13℃，T10%提升近43℃，质量残留率高达82.6wt%；空气氛围下，T_5%提升近36℃，T_10%提升近64℃，质量残留率高达83.1wt%。X-射线光电子能谱(XPS)及扫描电镜(SEM)结果表明在聚酰亚胺主链中引入碳硼烷笼状单元后在高温环境中易在材料表面形成氧化硼(B₂O

Preparation of polyimides containing carborane moiety and the thermal resistance mechanism

A series of polyimide materials were successfully prepared by embedding o-carborane cage structure into polyimide main chains. First, the diamine monomer (DNCB) containing o-carborane unit was designed and synthesized, and then copolymerized with 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-benzophenone tetracarboxylic anhydride (BTDA) to synthesize the polyamic acid (PAA) precursor solution. PAA films were prepared by solution casting method, and then polyimide films containing different contents of carborane unit were obtained after high-temperature thermal imidization. Thermogravimetric analysis (TGA) shows that the addition of DNCB significantly improves the thermal stability and thermal oxidation stability of polyimide materials. When the molar content of DNCB in all diamines reaches 40%, the temperature corresponding to 5wt% mass loss (T_5%) increases by nearly 13℃, T_10% increases by nearly 43℃ and the mass residual rate was as high as 82.6wt%. Under the air atmosphere, T_5% increases by nearly 36℃, T_10% increases by nearly 64℃, and the mass residual rate reaches as high as 83.1wt%. This is due to the oxidation of carborane cage and the formation of multi-layer passivation protective layer on the surface of the film, which prevents the degradation of internal polymer materials in contact with oxygen.