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 40oC (designated as {31) and-20oC (designated as {32), measured at 35Hz. The {31-transition was tentatively assigned to the micro-Brownian motion of the main chain in the amorphous phase rich in TrFE-units; the {32-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 B' ofTrFE-VDF copolymer took on a maximum at 55 mol% VDF content. The numerical value of B' was 15 (at l kHz and at 22°C) and about 1.7 times larger than those of poly(trifluoroethylene) and poly(vinylidene fluoride) homopolymers.

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