Solvent‐solubility‐parameter‐dependent homogeneity and sol–gel transitions of concentrated polyacrylonitrile solutions

ABSTRACT In this study, we systematically explored the dependence of the homogeneity and sol–gel transition temperatures of various polyacrylonitrile (PAN) solutions on the solvent solubility parameters. The Cole–Cole slope was used to characterize the solution homogeneity, and we found that the PAN/dimethyl sulfoxide (DMSO) solution, which had a smaller Hansen solubility parameter distance between the solvent and PAN, showed better solution homogeneity than the PAN/dimethylformamide and PAN/dimethylacetamide solutions. Additionally, we found that both heating and cooling were able to cause the gelation of the PAN solution, although their mechanisms were totally different. The gelation caused by heating was ascribed to the nitrile–nitrile coupling of PAN chains, whereas the gelation caused by cooling was due to the solvent bridge effect. In this case, DMSO, which had the highest polarity and the strongest interactions with nitrile groups, caused the highest gelation temperature of the PAN solution during cooling. The gelation temperature of the PAN solution exhibits dependence on its solvent polarity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45405.