Improved solubilization of pyromellitic dianhydride and 4,4′-oxydianiline in ionic liquid by the addition of zwitterion and their polycondensation

Solubility of 4,4′-oxydianiline and pyromellitic dianhydride as starting materials of polyimide in 1-benzyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide was significantly improved by the addition of imidazolium type zwitterion to afford high molecular weight polyimide.