Anionic Synthesis Of Poly(Acrylonitrile) And Its Copolymer Via Amine Compounds

Polyacrylonitrile (PAN), which has unique and well-known properties, is presently recognized as an important precursor for carbon fiber. Because of the quality of carbon fiber is strongly dependent on the molecular weights of precursor, extensive efforts have been taken to prepare high molecular weight PAN. Traditionally, commercial PAN is prepared by free radical polymerization using azodiisobutyronitrile (AIBN) and azobisisoheptonitrile (ABVN), it has been found that PAN with high molecular weight hardly be obtained because of uncontrollable reaction progress. Compared with the radical polymerization mentioned above, anionic polymerization has long been known as the best way to prepare polymer with high average molecular weight. However, normal anionic polymerization, which usually uses alkali metals as initiator, has a lot of drawbacks in synthesis of well-defined PAN. As a consequence of high reactivity, metal initiators tend to generate various side reactions. In addition, the introduced transition metal complex is harmful for carbonizing process, bringing defects and motley appearance to carbon fibers. To solve the problem, there were lots of efforts concerning on the research of Lewis base (LB) as new metal-free anionic initiator in recent years.In this study, some typical amine compounds such as DMAP, TBD and DBU were used as initiator in anionic polymerization of acrylonitrile. Effects of solvent, initiator concentration, reaction temperature and ammonium salt were thoroughly investigated and discussed. The results showed that DBU could efficiently initiate acrylonitrile at room temperature, producing polymers with extremely high molecular weight (Mw up to 1400,000 g/mol) and narrow distribution (Mw/Mn=1.3) in DMSO. The polymerization exhibits controlled characters:molecular weights of PAN increasing with the ratio of monomer to initiator and keeping narrow molecular weight distributions. In addition, the kinetics of polymerization was discussed and the reaction order, reaction rate and apparent activation energy were calculated, proving that the reaction rate would increase dramatically as the temperature rise.In order to reduce the heat release in the process of preoxidation, copolymerization of PAN was investigated on the basis of homo-polymerization system. MAN、MA、 AM、DMAM were used as comonomer in anionic polymerization of AN, it was found that DMAM appears to be the ideal comonomer, producing products with high molecular and narrow distribution. The configuration and thermodynamic properties were determined by FTIR、XPS、XRD、 GPC、TA、SEM, the results indicated that the temperature of cyclical reaction is significantly lower than homo-PAN, and has better spinnability.