INVESTIGATION OF BASE INDUCED CYCLIZATION AND METHINE PROTON ABSTRACTION IN POLYACRYLONITRILE SOLUTIONS

When polyacrylonitrile (PAN) solutions are treated with bases, coloration occurs. It has been proposed in the past that this is due to a cyclization reaction which leads to conjugated structures. In this research, the effect of bases of differing strength was systematically examined and an attempt made to determine the extent of cyclization, if it took place at all. The literature has also suggested that cyclization would occur preferentially in isotactic sequences. Hence tacticity changes after base treatment were monitored by in situ C-13 nuclear magnetic resonance experiments to test this model. Strong bases caused coloration, chain scission, partial inversion of configuration and gelation induced by crosslinking. By using sodium deuteroxide, it was shown that the methine proton could be abstracted by strong bases. Weak bases caused only coloration at room temperature, while heating was needed to induce tacticity changes and gelation. Contrary to previous suggestions, we found no evidence for cyclization even in red-black solutions. We concluded that the (unidentified) chromophore was present in very low concentrations but was very intense.