聚铝碳硅烷纤维预氧化过程组成结构演变的研究

采用热重-差热分析、元素分析、扫描电子显微镜、凝胶渗透色谱、红外光谱和核磁共振等手段, 研究了聚铝碳硅烷(PACS)纤维预氧化过程中组成、结构演变的规律和反应机理. 结果表明, 空气中PACS纤维从210 ℃左右开始与氧发生放热反应; 随着预氧化温度的升高, 纤维的氧含量逐渐增加, 凝胶含量在氧增重为6～8 wt%时急剧增加, 纤维表面出现细小的微裂纹. 预氧化初期, 主要是Si—H键与氧的反应, 生成Si—O—Si键, 纤维的数均分子量急剧增加, 形成交联结构; 预氧化中期, Si—H键继续反应, Si—O—Si结构明显增多, 同时Si—CH₃和Si—H与氧反应, 生成少量的Si—O—C结构; 预氧化后期, 纤维完全交联, 纤维中存在SiC₄, SiC₃H, Si—O—Si和少量的Si—O—C结构.

Evolution of Composition and Structure of Polyaluminocarbosilane Fiber during Curing Process

The evolution of composition and structure of polyaluminocarbosilane (PACS) fiber during curing process in air was investigated by TG-DTA, SEM, GPC, FT-IR, CP/MAS NMR techniques and chemical analysis. Results showed that the PACS fiber reacted with oxygen starting from about 210 ℃ in air and it was an exothermic reaction. The oxygen content in the fiber increased with the elevation of temperature. It was accompanied by a rapid increase of the gel content in the stage of the weight gain of 6～8 wt( and microflaw generated on the surface of the cured PACS fibers. In the initial stage, Si—H bonds in PACS reacted with oxygen to form Si—O—Si bonds and the of the PACS fiber increased greatly, which resulted in a cross-linked structure in the cured PACS fiber. In the medium stage, the remaining Si—H bonds continued to react with oxygen and the reaction between Si—CH₃, Si—H and oxygen took place producing Si—O—C groups. In the last stage, the fiber cross-linked completely and it consisted of SiC₄, SiC₃H, Si—O—Si and Si—O—C groups.