title: Determination of chain flip rates in poly(ethylene) crystallites by solid-state low-field 1H NMR for two different sample morphologies.
abstract: Using simple and cheap low-field (1)H NMR methods such as the magic sandwich echo technique and FID component analysis, we determine jump rates for 180° chain flips in poly(ethylene) (PE) crystallites, which are comparable to literature data obtained from advanced, complex, and time-consuming (13)C-based NMR methods. In the investigated temperature range, we find similar jump rates for the local chain flip process in a melt-crystallized sample containing lamellar crystals with disordered fold surface and in reactor powder samples having a rather adjacent-reentry-like structure. Previous NMR studies of Yao et al. revealed different chain diffusion coefficients for the resulting long-range chain diffusion between amorphous and crystalline regions in melt- vs solution-crystallized (adjacent reentry) samples. From our results, we conclude that, in the investigated temperature range, the fold surface, which presumably influences the effective chain transport, does not have a strong effect on the time scale of the local chain flip process. We confirm an Arrhenius temperature dependence of the jump rate for the local flip process and calculate activation energies which show a slight trend toward smaller values for the reactor powders (~76 kJ/mol) in comparison to the melt-crystallized sample (~103 kJ/mol).
authors.affiliation: Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Bärenwald
authors.forename: Y
authors.initials: Y
authors.lastname: Champouret
authors.forename: K
authors.initials: K
authors.lastname: Saalwächter
authors.forename: K
authors.initials: K
authors.lastname: Schäler