Theory of dielectric crystalline dispersion in high polymers

Abstract

Theoretical investigation was attempted for the dielectric crystalline dispersion which is observed at high temperatures in highly crystallized polymer samples such as polypropylene and oxidized polyethylene. The dielectric dispersion of this kind had been confirmed experimentally to come from the crystalline part, but no theoretical investigation had been reported for this dielectric dispersion. The proposed mechanism was such that this dielectric dispersion is attributed to the dipole polarization due to torsional and longitudinal motions of skeletal chains in polymer crystallites. On the basis of such a mechanism, the expression of the complex dielectric constant was calculated by solving theBoltzmann equation for the motion of the skeletal chain. The magnitude of the absorption, its temperature dependence and the shape of the absorption curve were derived from the complex dielectric constant. The activation energy was also calculated by the use of Frohlich's method. The agreement between the theoretical results and the observed data seems quantitatively good, which seems to show the appropriateness of the present mechanism for the dielectric dispersion of this sort. The observed data up to date are, however, given as the tan δ vs. temperature curve, in which might be included in the effect of the structural alteration such as the recrystallization. The observation by varying the frequency at constant temperatures seems to be desirable for being compared with the present theory.