Sol-gel transition of poly(1,1-difluoroethylene) in γ-butyrolactone/cyclohexanone mixed solvent

Poly(1, 1-difluoroethylene) (hereafter named poly(vinylidene fluoride) (PVdF)) in the mixed solvent of gamma-butyrolactone/cyclohexanone converts to thermally reversible gel. Gelation process of PVdF in the mixed solvent was investigated by Fourier transform infrared(FT-IR) measurement and gelation time (t(gel)) was measured as a function of composition of cyclohexanone (X(cyclo)) in the mixed solvent. FT-IR spectra suggested that gelation of PVdF in gamma-butyrolactone/cyclohexanone mixed solvent occurred through crystallization of polymers taking two Binds of conformations, T(3)GT(3)(G) over bar and TGT (G) over bar. t(gel) increased slowly with increasing X(cyclo), and showed maximum value at X(cyclo) = 30 vol%, then decreased with increasing X(cyclo) According to measurement of cloud temperature of PVdF solution, the mixed solvent showed the maximum solvent power at X(cyclo) = 30 vol%. That is, cosolvency appeared at this composition. It is considered, therefore, that crystallization and gelation of PVdF in the mixed solvent proceed very slowly at X(cyclo) =30 vol%.