Sol-Gel Transition Curve of Poly(vinylidene fluoride) in Organic Solvents

Abstract

It is well known that poly(1, 1-difluoroethylene)(hereafter named poly(vinylidene fluoride)(PVdF)) dissolved in some ketones or lactones at high temperature forms a thermoreversible gel in the vicinity of room temperature. In this study, the interaction parameter(x₁₂) between PVdF and solvent was estimated as a function of temperature by an inverse gas chromatography(IGC) method. The correlation between gelation of PVdF solution and the magnitude of x₁₂ value was discussed. The solvents used were hexane, cyclohexanone, γ-butyrolactone, and N, N-dimethylformamide. Moreover, sol-gel transition curve was determined for four samples with different molecular weights.
The interaction parameter x₁₂ obtained for each PVdF/solvent system increased slowly with decreasing temperature. The gelation of PVdF occurred with decreasing temperature for the following two systems: one was the system where the parameter x₁₂ increased passing through 0.5 such as the system PVdF/cyclohexanone; the other was the system where x₁₂ approached 0.5 such as the system PVdF/γ-butyrolactone. The sol-gel transition curve shifted to lower concentration with increasing molecular weight.