群子统计理论研究PAN预氧化过程的成环机理

A theoretical study of the cyclization of polyacrylonitrile during the pre-oxidation process using sub-cluster statistics theory

将通过自由基聚合得到的聚丙烯腈(PAN)在不同温度下进行预氧化反应,借助X射线衍射(XRD)分析,根据群子统计理论,研究了PAN在预氧化过程中从线形结构到环形有序结构转变的机理,求出了预氧化反应过程中的活化能,探讨了PAN在预氧化过程中成环和成线的竞争关系。研究结果表明,在250～300℃范围内,预氧化温度越高,越容易进行成环反应,环化度越高;预氧化过程中环化活化能为63.57kJ/mol,成环反应不占优势,环状结构与线性结构共存,PAN只有进一步高温炭化,才有可能使更多的线性结构转化为环状结构。

Polyacrylonitrile was obtained by radical polymerization after pre-oxidation at different temperatures. A micro-structural transformation during the pre-oxidation step, from the fibrous linear structure to a cyclic structure, was observed by XRD. The activation energy of that process was calculated, and the mechanism investigated using sub-cluster statistics theory. The competitive relationship between cyclization and linearization during the pre-oxidation step was studied. The results show that in the temperature range 250 to 300 ℃, the degree of ring formation increased with increasing pre-oxidation temperature. The activation energy of the cyclization reaction in the pre-oxidation process is 63.57 kJ/mol, showing that the cyclization reaction is not favorable. Cyclic structures and linear structures co-exist in this temperature range and further high-temperature carbonization is necessary in order to convert all of the linear form into cyclic structures.