Backbone Dynamics of the Nafion Ionomer Studied by ¹⁹F‐¹³C Solid‐State NMR

Abstract

The chain dynamics of a perfluorinated ionomer, Nafion®, have been studied by 19F and 19F‐13C 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 19F‐13C dipolar couplings and chemical shift anisotropies (CSAs) that are linearly correlated. Additional narrowing of the CSAs indicated that the backbone axis in hydrated Nafion moves with an amplitude >15°. Motional amplitudes of various backbone and side‐branch sites were inferred from motionally averaged 19F CSA parameters measured with CSA recoupling. They increase with the distance from the branch point, e.g., to >25° in the center of the side branch. Implications for the chain and supramolecular structure of Nafion are discussed.magnified image

Constitutive response and mechanical properties of PFSA membranes in liquid water

“…PFSA membranes have a PTFE-like backbone with attached perfluorinated side chains [32,[64][65][66]. Thus, by assuming that the PTFE-like backbone of the swollen PFSA membrane exhibits simi lar deformation behavior to that of PTFE, we can explain some of our experimental observations for the PFSA membrane by using the reported data on the mechanical behavior of PTFE [67][68][69][70][71].…”

Tetrafluoroethylene Copolymers with Sulfonyl Fluoride Pendants: Syntheses in Supercritical Carbon Dioxide, Polymerization Behaviors, and Properties

“…When PSVE segments are incorporated into the polymer chains, equally weak signals at the same positions due to the two CF groups in the backbone and side groups are observed, as suggested previously. [30,31] The signal near -112 ppm in the precursor copolymer is assigned to the 19 F nuclei in the CF 2 group near SO 2 F group, by comparison with a similarly situated CF 2 group in PSVE monomer. And it is also assignable to the four fluorines of the backbone CF 2 groups next to the OCF branch point.…”

Structure-property relationship in ionomer membranes

“…This model has been shown to capture the experimental scattering curves better than spherical cluster-channel models at high water contents [7]. Also, the nanostructure of a highly-swollen PFSA membrane has been shown to be comprised of repeating PTFE units, similar to the helical molecular structure of PTFE, surrounding the water domains [14,19,58]. In light of these results, we propose an alternative model for highly-swollen PFSA membrane: cylindrical water domains surrounded by polymer backbone in hexagonal RVEs (Fig.…”