The Flory-Huggins interaction parameter and thermoreversible gelation of poly(vinylidene fluoride) in organic solvents

Abstract

The Flory-Huggins interaction parameter (χ12) between poly(vinylidene fluoride) (PVdF) and organic solvent was estimated experimentally over wide range of temperature by an inverse gas chromatography (IGC) using many kinds of solvents such as alkane, alkene, ketone, lactone, and nitrogen-containing solvent. The thermoreversible gelation of PVdF solution was discussed from the magnitude of interaction parameter χ12 PVdF and solvent. The parameter χ12 was measured for a concentrated PVdF solution by the usual IGC technique. The parameter χ12 obtained for each PVdF/solvent system increased slowly with decreasing temperature. The present systems were divided broadly into three groups according to the magnitude of χ12 in the vicinity of room temperature, i.e., group (a) with χ12 ≫ 0.5, group (b) with χ12 ≈ 0.5, and group (c) with χ12 ≪ 0.5. The group (b), to which ketone and lactone belong, converted to thermoreversible gels accompanying with crystallization of polymer. The gelation process of PVdF solution was investigated through measurement of in situ Fourier transform infrared (FT-IR) spectroscopy. The time-resolved FT-IR spectra suggested that the gelation took place taking the conformation T3GT3Ḡ for the system where the parameter χ12 was nearly equal to 0.5 such as PVdF in γ-butyrolactone. For the system where the parameter χ12 became larger than 0.5 such as PVdF in cyclohexanone, 3-pentanone, 3-hexanone, or 3-octanone, the getation occurred taking the conformation TGTḠ.