Thermoreversible gelation of poly(vinylidene fluoride) in diethyl adipate: A concerted mechanism

Poly(vinylidene flouride) (PVF2) gels in diethyl adipate (DEA) with fibrillar morphology. The gels are transparent. The Wide-angle X-ray scattering pattern and FT-LR spectra of the gel indicate the presence of solvated alpha-phase PVF2 crystallites in the gel. The intensities of the X-ray diffraction peaks of the gel are mostly different than those of the melt-crystallized sample. The plots of enthalpy of gel fusion and enthalpy of gel formation with a weight fraction of PVF2 (W-PVF2) indicate a positive deviation from linearity. Analysis of these results indicates polymer-solvent complex formation in the molar ratio of 1:2 for the DEA and PVF2 repeating unit, respectively. The phase diagram also supports polymer-solvent complex formation with an incongnrent melting point. The gelation kinetics is studied by the test tube tilting method. Analysis of the concentration function of the gelation rate supports the theory that this gelation process obeys the three-dimensional percolation mechanism. The temperature coefficient analysis is done both by the Flory and Weaver theory of coil-to-helix transtion and by the growth rate theory of fibrillar crystallization extended to the polymer-diluent system. A comparison of energy barrier values of both the processes indicates that the gelation is a concerted process of conformational ordering and crystallization.