Transition Behavior and Dielectric Properties in Trifluoroethylene and Vinylidene Fluoride Copolymers

Abstract

The transition behavior and dielectric properties of trifluoroethylene (TrFE)–vinylidene fluoride (VDF) copolymers were studied. The DSC and X-ray diffraction measurements indicated that the conformation of the polymers was in a crystalline state throughout the entire polymer composition, and crystallized isomorphically. In the thermal expansion measurement of the 56:44 TrFE–VDF copolymer, two breaks were observed, indicating two glass-to-rubber transitions. These two transitions were also observed in a mechanical relaxation study with peaks at 40°C (designated as β1) and −20°C (designated as β2), measured at 35 Hz. The β1-transition was tentatively assigned to the micro-Brownian motion of the main chain in the amorphous phase rich in TrFE-units; the β2-transition was assigned to the micro-Brownian motion of the main chain in the amorphous phase, rich in VDF-units. It was also found that the dielectric constant e′ of TrFE–VDF copolymer took on a maximum at 55 mol% VDF content. The numerical value of e′ was 15 (at 1 kHz and at 22°C) and about 1.7 times larger than those of poly(trifluoroethylene) and poly(vinylidene fluoride) homopolymers.