含水均相溶液聚合制备高品质聚丙烯腈及其性能研究

The significant approach to manufacture high performance polyacrylonitrile (PAN) fibers is adopting high-quality PAN copolymers as solute to prepare spinning dope. Compared to the conventional heterogeneous solution polymerization and aqueous precipitation polymerization, ammonium persulphate (APS) will be employed as the initiator in this project. Mixed solvents of dimethyl sulfoxide and water (with its weight fraction less than 10%) will be adopted as the reaction medium. Copolymerizations of acrylonitrile and vinyl monomers will be investigated by the polymerization technique named as containing water homogeneous solution polymerization (CWHSP). Introduction of less water during the polymerization process is propitious to reduce probability of chain transfer reactions. It is also favorable to promote occurrence of gelation acceleration phenomenon. All these factors are beneficial to prepare high-quality PAN copolymers with high polymerization conversion, high molecular weight and appropriate molecular weight distribution. At the same time, the homogeneous character is retained, which expands selectivity of its subsequent spinning process. Effects of various polymerization factors, especially the existence of less water, on the polymerization will be investigated through various measuring methods, such as Ubbelohde viscometer, gel permeation chromatograph, differential scanning calorimeter, thermogravimetric analysis, element analysis, Fourier transform infrared spectroscopy, wide angle X-ray diffraction, static/dynamic rheometer, etc. Structures and properties of the obtained PAN polymers will be studied, whose relationships with the parameters of polymerization technology, will be also discussed. And valuable theoretical achievements applied to industrialized production stage of carbon fibers will be acquired.

采用高品质聚丙烯腈（PAN）共聚物进行纺丝是制备高性能PAN原丝的重要途径。与传统的均相溶液聚合和水相沉淀聚合不同，本项目拟采用含水均相溶液聚合（CWHSP）工艺，以过硫酸铵（APS）为引发剂，以二甲基亚砜（DMSO）/水（质量含量不超过10%）混合溶剂为反应介质，进行丙烯腈（AN）与乙烯基单体的共聚合反应。少量水的引入降低了链转移反应几率，促进了凝胶化自加速现象发生，有利于制备出具有高转化率、高分子量和合适分子量分布的PAN共聚物。同时保证反应体系的均相聚合特征，扩大了其后续纺丝工艺的选择性。借助乌氏黏度计、凝胶渗透色谱、差示扫描量热分析、热重分析、元素分析、傅里叶变换红外光谱、广角X射线衍射和静/动态流变等多种测试方法，探讨各聚合工艺参数，尤其是少量水的存在对聚合反应的影响规律，以及它们与PAN产物结构和性能之间的相互关系，希望获得可应用于碳纤维工业化生产的有价值的理论成果。

聚丙烯腈（PAN）是制备碳纤维最重要的前驱体，性能优异的PAN纺丝原液是制备优质PAN原丝的前提。为了解决均相溶液聚合较短时间不宜制得高分子量PAN共聚物和非均相沉淀聚合工艺后续纺丝工艺繁琐的问题，本项目采用混合溶剂法制备PAN共聚物，兼具均相溶液聚合和水相聚合的优点，能够制备出高性能的PAN共聚物，有利于获得高品质的PAN原丝。在混合溶剂法制备PAN共聚物的工艺选择过程中，以过硫酸铵（APS）和偶氮二异丁脒盐酸（V50）为引发剂，以有机溶剂和水为混合反应介质，采用含水均相溶液聚合（CWHSP）工艺，通过调整不同的聚合工艺参数，成功制得分子量较高且可控以及分子量分布合适的高品质PAN共聚物。. 结果表明：（1）对于采用V50引发的CWHSP体系中，当有机溶剂为二甲基甲酰胺（DMF）时，分子量明显较低，因此采用二甲基亚砜（DMSO）为溶剂。随着水含量的增加，转化率先增加后减少，黏均分子量处于18~20万之间。当混合溶剂比为94:6时，制得转化率58.6%、黏均分子量18.6万、分子量分布1.6的高品质PAN聚合物；（2）在APS引发聚合的含水均相混合体系中，当只有溶剂DMSO时，反应体系黏度较大，随着混合溶剂中的水含量增加，聚合反应时间延长，引发剂浓度变大，聚合体系容易产生凝胶，得到聚合物溶液成膜性变差。加入DMF后，使得反应体系黏度变小，成膜性变好，随着DMF含量的减少，转化率没有明显变化，分子量则逐渐上升。（3）对CWHSP制得PAN聚合物的结构与性能研究表明，随着衣康酸（IA）用量的增加，PAN聚合物中O元素含量增加，说明IA在分子链中含量增加。同时，傅里叶变换红外（FTIR）图谱中代表IA链节的1735 cm-1处的C=O基团峰的强度增大。与PAN均聚物相比，PAN共聚物的放热峰宽度变大，IA的加入缓和了环化反应。. 与采用水溶性引发剂的水相沉淀聚合和混合溶剂沉淀聚合工艺相比，CWHSP工艺可制备出分子量范围较宽的PAN共聚物，且其分子量分布较窄。少量水的使用在后续纺丝溶液的处理过程中，可起到一定的凝胶化作用，这为凝胶纺丝提供了一个新途径，扩大了PAN纺丝工艺的选择范围。由此可见，CWHSP工艺可行且潜力巨大，极大地丰富了PAN的合成途径，有望成为制备高性能碳纤维的方法之一。