Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR

Materials

Todd M. Alam⁶  Janelle E. Jenkins⁶  Dan S. Bolintineanu³  Mark J. Stevens²  Amalie L. Frischknecht²  C. Francisco Buitrago⁴  Karen I. Winey¹  Kathleen L. Opper⁵ 

[1] Dept. of Material Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA; E-Mail:;Computational Materials Science and Engineering Department, Sandia National Laboratories, Albuquerque, NM 87185, USA; E-Mails:;Department of Nanoscale and Reactive Processes, Sandia National Laboratories, Albuquerque, NM 87185, USA; E-Mail:;Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA; E-Mail:;DuPont Central Research and Development, Wilmington, DE 19880-0302, USA; E-Mail:;Department of Nanostructured and Electronic Materials, Sandia National Laboratories, Albuquerque, NM 87185, USA; E-Mail:

关键词: MAS NMR;    REDOR;    lithium ionomer;    precise polymer;    ionomer;   

DOI  :  10.3390/ma5081508

来源: mdpi

【 摘 要 】

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.

【 授权许可】

CC BY   
© 2012 by the authors; licensee MDPI, Basel, Switzerland.