Thermoreversible Gelation of a Vinylidene Fluoride‐Based Copolymer in Methyl Ethyl Ketone: Dynamics and Structure

Abstract

Thermoreversible poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐co‐HFP)) gels are formed in an aliphatic ketone − methyl ethyl ketone (MEK) − at high concentrations (above 11 wt%). This gelation phenomenon is first investigated in terms of gelation kinetics which is found to depend strongly on both copolymer concentration and temperature. Melting temperatures Tm of P(VDF‐co‐HFP)‐based gels prepared at different concentrations, in MEK are measured by DSC. Combination of 19F Nuclear Magnetic Resonance (NMR), Small‐Angle X‐ray Scattering (SAXS), and Wide‐Angle X‐ray Scattering (WAXS) on undried/nonlyophilized gels is used to probe both the gelation mechanisms and the structure of these systems. 19F NMR experiments allow studying selectively the fluorinated copolymer. The occurrence of a polymer network‐like structure with rigid zones acting as cross‐links has been highlighted. Such a behavior is only observed in the gel state: no polymer network or rigid zones exist when the polymer–solvent system is in the liquid state. Moreover, the fraction of rigid zones as well as the fraction of elastically active chain portions increases with the copolymer concentration. The nature, of the rigid zones present within the gels are investigated by X‐ray diffraction. Rigid regions are found to display a crystalline order.