Backbone dynamics of the Nafion ionomer studied by F-19-C-13 solid-state NMR

TitleBackbone dynamics of the Nafion ionomer studied by F-19-C-13 solid-state NMR
Publication TypeJournal Article
Year of Publication2007
AuthorsChen Q, Schmidt-Rohr K
Journal TitleMacromolecular Chemistry and Physics
Volume208
Pages2189-2203
Date PublishedOct
Type of ArticleArticle
ISBN Number1022-1352
Accession NumberISI:000250351900014
Keywords2-DIMENSIONAL EXCHANGE NMR, 2-TIME DISTRIBUTION-FUNCTIONS, c-13 nmr, CENTERBAND-ONLY DETECTION, defects, FORCE-FIELDS, GLASS-TRANSITION, HELIX REVERSAL, HOMONUCLEAR DIPOLAR, nuclear-magnetic-resonance, POWDER, SAMPLES
Abstract

The chain dynamics of a perfluorinated ionomer, Nafion (R), have been studied by F-19 and F-19-C-13 solid-state NMR at 295 K. The backbone of Nafion is essentially poly(tetrafluoroethylene) (PTFE), which was investigated for reference. Fast uniaxial rotations of the helical backbone were confirmed in PTFE and detected similarly in Nafion, though with a distribution of amplitudes. The rotations produce motionally averaged F-19(-13) C dipolar couplings and chemical shift anisotropies (CSAs) that are line-arly correlated. Additional narrowing of the CSAs indicated that the backbone axis in hydrated Nafion moves with an amplitude >15 degrees. Motional amplitudes of various backbone and side-branch sites were inferred from motionally averaged F-19 CSA parameters measured with CSA recoupling. They increase with the distance from the branch point, e.g., to >25 degrees inthecenteroitheside branch. Implications for the chain and supramolecular structure of Nafion are discussed.

DOI10.1002/macp.200700200
Alternate JournalMacromol. Chem. Phys.