NMR study of chain orientation in drawn poly (vinylidene fluoride) films. I: The effects of poling on the double orientation distribution function

The double orientation distribution function (DODF) of the chains in the drawn film of PVDF was determined by the NMR second-moment dependence on the angle φ between the magnetic field H 0 and the normal to the film surface. The Fourier coefficient a 2 of DODF determined for the unpoled sample changed from -0.24 to 0.28 on poling, but a 4 =0.08 did not change. These values were obtained from the highly oriented noncrystalline and crystalline parts in the drawn film. By using the Fourier coefficients a 2 m c ( m =1, 2) of the DODF of the b -axis for the crystalline part in the poled sample obtained by the X-ray diffraction method, the Fourier coefficients a 2 m or ( m =1, 2) of the DODF in the highly oriented non-crystalline part were estimated to be a 2 or =0.3 and a 4 or =0.24 at 18degC. The invariant of a 4 was explained in terms of the DODF of the noncrystalline chains which are aligned preferentially upon poling with the chain dipoles oriented normally to the film surface. This paper discusses the molecular motion in the highly oriented noncrystalline part due to the temperature dependence of these coefficients.