Abstract
The carboxylic acid proton and the lithium coordination environments for precise and random Li-neutralized polyethylene acrylic acid P(E-AA) ionomers were explored using high speed solid-state 1H and 7Li MAS NMR. While the 7Li NMR revealed only a single Li coordination environment, the chemical shift temperature variation was dependent on the precise or random nature of the P(E-AA) ionomer. The 1H MAS NMR revealed two different carboxylic acid proton environments in these materials. By utilizing 1H-7Li rotational echo double resonance (REDOR) MAS NMR experiments, it was demonstrated that the proton environments correspond to different average 1H-7Li distances, with the majority of the protonated carboxylic acids having a close through space contact with the Li. Molecular dynamics simulations suggest that the shortest 1H-7Li distance corresponds to un-neutralized carboxylic acids directly involved in the coordination environment of Li clusters. These solid-state NMR results show that heterogeneous structural motifs need to be included when developing descriptions of these ionomer materials.
Highlights
Ionomers are polymers containing low concentrations (
The increase in the acid 1H nuclear magnetic resonance (NMR) chemical shifts for the Li-neutralized ionomers reveals a strengthening of the hydrogen bond strength in comparison to the COOH cyclic dimer
The 1H-7Li rotational echo double resonance (REDOR) magic angle spinning (MAS) NMR response for the p9AA-43%Li ionomer with increasing recoupling times is shown in Figure 4, and was used to extract the dipolar coupling strength based on a
Summary
Ionomers are polymers containing low concentrations (
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