Comparative study of dielectric,mechanical, and nuclear magnetic relaxations of linear polyethylene. I. Broad-line NMR investigation of the fine structure of the α and γ loss bands observed by dielectric and mechanical measurements

Detailed investigation of the linewidth, second moment, and mobile fraction by straightline decomposition of NMR spectra of linear polyethylene from ca. ?160 to ca. 100°C reveals five molecular processes denoted γ₁, γ₂, β, α′, and α. Relaxation maps show that the γ₁, γ₂, and β processes correspond to the dielectric and mechanical relaxations given the same names, while the α and α′ processes correspond respectively to the mechanical α₂ process due to molecular motion in the interior of crystals and to the dielectric α process. Close relations are found between the mass fractions of protons for the γ₁ and β processes and also between those for the γ₂ and α′ processes. From the effects of diluent on these processes and the annealing-time dependence of mass fractions of protons, the γ₁, and β processes are attributed to two modes of molecular motion in an interlamellar amorphous region, while the γ₂ and α′ processes are attributed to motions in the lamellar surface layers. The surface-layer thickness obtained by applying the two-phase model for the data on mobile fraction agrees quite well with that reported in the literature. The Bergmann–Nawotki three-component analysis of NMR spectra and symmetric-line decomposition for determining mobile fraction are shown to be unsuitable for studying the fine structure of the α and γ loss bands.