Dielectric behavior of copolymers of vinylidene fluoride and tetrafluoroethylene

Dielectric behavior and related bulk properties have been studied on copolymers of vinylidene fluoride (VDF) and tetra-fluoroethylene (TFE) with TFE contents of 10 to 30 mol-%, Dielectric properties of copolymers did not vary much with TFE contents. Copolymers exhibited the dielectric relaxation similar to that as found for poly(vinylidene fluoride) (PVDF) at low temperature which was connected with micro-Brownian motions of the molecular chain backbone in amorphous regions. Variation of the relaxation frequency with temperature in the vicinity of the glass transition was fitted by the modified WLF equation. No noticeable dielectric loss peak associated with the relaxation in crystalline regions in form I1 of PVDF was found at high temperature. This may be understood because the VDF-TFE copolymer has the same structure as form I of PVDF. The dielectric constant and loss increased with increasing temperature and/or decreasing frequency above room temperature owing to the space charge polarization of ionic impurity.