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.
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Alam, T.M.; Jenkins, J.E.; Bolintineanu, D.S.; Stevens, M.J.; Frischknecht, A.L.; Buitrago, C.F.; Winey, K.I.; Opper, K.L.; Wagener, K.B. Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR. Materials 2012, 5, 1508-1527.
Alam TM, Jenkins JE, Bolintineanu DS, Stevens MJ, Frischknecht AL, Buitrago CF, Winey KI, Opper KL, Wagener KB. Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR. Materials. 2012; 5(8):1508-1527.
Alam, Todd M.; Jenkins, Janelle E.; Bolintineanu, Dan S.; Stevens, Mark J.; Frischknecht, Amalie L.; Buitrago, C. Francisco; Winey, Karen I.; Opper, Kathleen L.; Wagener, Kenneth B. 2012. "Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR." Materials 5, no. 8: 1508-1527.