Ferroelectric Transition in Vinylidene–Trifluoroethylene Copolymer Studied by Nuclear Magnetic Resonance Method

Abstract

NMR absorption lines for a uniaxially drawn film of VDF–TrFE copolymer (72:28) were measured as a function of the alignment angle γ between the drawn axis and the magnetic field, over a temperature range from 23 to 130°C. The line shape consisted of inner, intermediate and outer peaks below the Curie temperature Tc. The line width of the intermediate peak narrowed at about 40°C with increasing temperature, and above 80°C it increased gradually by 1—3 Oe up to Tc. This line width as well as the line width of the outer peak strongly depended on γ, indicating that the nuclear dipole interactions in the crystalline region contribute to these peaks. Above Tc the width of the outer peak and the second moment decreased markedly owing to the chain motion accompanying conformational changes from the all-trans sequence to the combination of TG, TḠ, T3G, and T3Ḡ groups. The remarkable γ-dependence of the line shape as well as the line width observed in the paraelectric phase may be interpreted by a one-dimensional diffusion motion of conformational defects, and compared well with the ESR of a one-dimensional magnetic substance (CH3)4 NMnCl3 (TMMC).