辐射引发和热引发聚丙烯腈纤维的自由基研究

利用电子自旋共振波谱(ESR)研究了聚丙烯腈(PAN)纤维在真空以及空气气氛下经γ射线辐射引发和热引发产生的自由基. 结果显示，室温下辐射诱导产生的自由基为烷基自由基和聚亚胺自由基，辐射产生的自由基随温度升高而衰减，150 ℃时完全消失. 热引发的自由基则依赖于温度和氧气， 当PAN纤维在空气中加热至190 ℃时，开始产生多烯自由基，而且自由基浓度随温度升高而迅速增加；在真空条件下，PAN纤维经加热只产生极少量自由基. 据此推断，热引发自由基是通过热氧化反应产生的，这类自由基位于共轭结构上，其共轭长度也随温度的升高而增加.

Radiation-and Thermal Treatment-Induced Radicals in Polyacrylonitrile Fibers Studied by ESR

The free radicals in polyacrylonitrile (PAN) fibers induced by γ-ray irradiation and thermal treatment were studied using electron spin resonance (ESR) technique. The radicals produced by radiation in air and vacuum at room temperature were assigned primarily to alkyl (H abstraction from methine) and polyimine radicals. These radicals were found stable at room temperature, but decayed with increasing temperature in air until 150 ℃. A new type of radical was formed in original PAN fibers at 190 ℃ in air, and the concentration of the radical increased significantly with temperature. Much less radicals were formed if the PAN fibers were heated in vacuum. It could be speculated that the new type of radical observed was related to thermal-oxidation reactions. This type of radical was attributed to a polyenyl radical located on the conjugated structure, and the conjugation length increased with temperature.