Analysis of anisotropy in dielectric absorption due to defects in the polyoxymethylene crystal

The dielectric absorption due to terminal polar groups localized in defect regions of polyoxymethylene crystals shows an anisotropy relative to an applied field. An attempt to interpret this anisotropy has been made by applying the barrier theory of Hoffman. The potential energy map for the rotation of the terminal polar group calculated from conformational analysis gives two minima. The angle between the dipole moment of the terminal OH and the fiber axis calculated in terms of the two conformations corresponding to the potential energy minima is in good agreement with results from infrared dichroism. This agreement is considered as evidence that the conformational analysis is reliable for estimating the potential energy minima required in the calculation according to the barrier theory. The barrier height obtained by the conformational analysis and the anisotropy calculated from the components of the dipole moments for the terminal polar group in terms of the barrier theory are in qualitative agreement with the experimental data.