Sol-gel transitions of poly(vinylidene fluoride) in organic solvents containing LiBF4

Poly(vinylidene fluoride) (PVdF) dissolved in organic solvents containing lithium tetrafluoroborate (LiBF4) forms stable gels when the solution is cooled to room temperature. Here, we describe the effects of LiBF4 concentration and different gelation solvents on the gelation process, and characterize the resulting structural morphology using several techniques. Diethyl carbonate (DEC), propylene carbonate (PC) and gamma-butyrolactone (GBL) were used as gelation solvents. Time-resolved Fourier transform infrared spectroscopic measurements showed that the conformational transition from TGT (G) over bar to T(3)GT(3)(G) over bar G occurred with the addition of lithium salts to the PVdF/DEC gel. In addition, PVdF produces thermoreversible gels in GBL and PC containing LiBF4, by assuming a T(3)GT(3)(G) over bar conformation regardless of the LiBF4 concentration. Scanning electron microscopy studies have indicated the presence of spherulites in the gels. Spherulite size decreased with increasing LiBF4 concentration, whereas gel-melting temperatures increased with an increase in LiBF4 concentration. These results indicate that gelation of PVdF in the presence of LiBF4 occurs as polymer chains assuming the T(3)GT(3)(G) over bar conformation, imparting the resulting gels with increased thermal stability. Polymer Journal (2011) 43, 540-544; doi:10.1038/pj.2011.21; published online 13 April 2011