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

Abstract

Abstract 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 γ 1 , γ 2 , β, α′, and α. Relaxation maps show that the γ 1 , γ 2 , 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 α 2 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 γ 1 and β processes and also between those for the γ 2 and α′ processes. From the effects of diluent on these processes and the annealing‐time dependence of mass fractions of protons, the γ 1 , and β processes are attributed to two modes of molecular motion in an interlamellar amorphous region, while the γ 2 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.