Abstract: The characteristics of molecular motion of the vinylidene fluoride (73)/trifluoro ethylene(27)copolymer ferroelectric have been investigated by dielectric relaxation measurements at low temperatures and low frequencies. With increase of the crystallinity of the copolymer, the Curie-point temperature T_c decreased and the dielectric constant increased in the region of ferroelectric-paraelectric phase transition. The frequency spectra of the copolymers below room temperature consisted of a low-frequency part ascribed to the micro-Brownian motion of molecular segments in the noncrystalline regions and a high-frequency part designated as the local motions of small-scale segments. The T_g(=-37℃) and △H(=48.8kJ/mol) of copolymers were obtained from the fitted results using two Cole-Cole functions and calculation with WLF equation and Arrhenius formula respectively.

Key words: vinylidene fluoride, trifluoroethylene, copolymer, molecular motion, dielectric relaxation