不同气氛下聚丙烯腈纤维中官能团的化学反应性

Chemical reaction characters of functional groups in polyacrylonitrile fibers heat-treated in air and nitrogen

在空气和氮气条件下,分别对聚丙烯腈(PAN)原丝在190～260℃范围内进行热处理,利用DSC、FT-IR、NMR与TG研究了PAN纤维的各官能团在不同介质中的化学反应性和化学结构演变。研究表明,不同气氛导致PAN大分子官能团的化学反应类型、反应程度和最终化学结构不同,氮气气氛下,热引发自由基化学反应的活化能较高,但反应速率快,氰基成环、亚甲基脱氢后逐渐异变生成C=CH—C=NH共轭结构;空气气氛下,热和氧引发离子环化反应的活化能较低,但反应速率慢,氰基成环、亚甲基脱氢、氧化反应生成含C=O、C=N的芳杂环结构;尽管氮气中成环及脱氢反应程度高,但氧化性气氛形成的含氧芳杂环结构热稳定性远大于氮气气氛下形成的共轭结构。

Chemical reaction behavior and chemical structure evolution of functional groups in polyacrylonitrile fiber heat-treated at 190 to 260 ℃ under air and nitrogen atmosphere were investigated by differential scanning calorimetry （DSC）, Fourier transform infrared spectrometry（FT-IR） , nuclear magnetic resonance （NMR） and thermogravimetry （TG）. Results show that the reaction atmosphere determines reaction type, reaction degree and structure of heat-treated PAN fiber. Under nitrogen condition, the heating triggers free radical chemical reaction, which is quicker and needs higher activation energy to generate the C = CH=C = NH conjugate structure due to dehydrogenation and nitriles base cyclization. Under air condition, the heating and oxygen cause ionic cyclization, which is slower and needs lower activation energy to generate aromatic heterocyelie structure containing C = O and C = N groups with super thermostability.