- R. Bärenwald, Y. Champouret, K. Saalwächter, K. Schäler.
Determination of chain flip rates in poly(ethylene) crystallites by solid-state low-field 1H NMR for two different sample morphologies.
J. Phys. Chem. B 116, 13089-97.
Using simple and cheap low-field 1H 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 timeconsuming
13C-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 solutioncrystallized
(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).