Ion Transport in Dynamic Polymer Networks Based on Metal–Ligand Coordination: Effect of Cross-Linker Concentration

Abstract

The development of high-performance ion conducting polymers requires a comprehensive multi-scale understanding of the connection between ion-polymer associations, ionic conductivity, and polymer mechanics. We present polymer networks based on dynamic metal-ligand coordination as model systems to illustrate this relationship. The molecular design of these materials allows for precise and independent control over the nature and concentration of ligand and metal, which are molecular properties critical for bulk ion conduction and polymer mechanics.The model system investigated, inspired by polymerized ionic liquids, is composed of poly(ethylene oxide) with tethered imidazole moieties that facilitate dissociation upon incorporation of nickel (II) bis(trifluoromethylsulfonyl)imide. Nickel-imidazole interactions physically crosslink the polymer, increase the number of elastically active strands, and dramatically enhance the modulus. In addition, a maximum in ionic conductivity is observed due to the competing effects of increasing ion concentration and decreasing ion mobility upon network formation. The simultaneous enhancement of conducting and mechanical properties within a specific concentration regime demonstrates a promising pathway for the development of mechanically robust ion conducting polymers.3

Multivalent ion conduction in solid polymer systems

“…Recent work from our group has shown that ion-conducting polymer networks form through the interaction of Ni 2+ salts with imidazole ligand coordination sites on a polymer chain. 67 At all studied salt concentrations, a dynamically crosslinked network was formed, showing the typical rheological signature of a plateau in the storage modulus, followed by subsequent liquid-like relaxation at lower frequencies. The plateau modulus increases as a function of salt concentration but saturates at around eight times the original value of 1 MPa upon complete crosslinking of the gel.…”

“…66 Such behavior is seen in a number of multivalent polymer systems, including both those with ether oxygens as the primary solvating units and those with different ion-polymer interactions such as Ni 2+ -imidazole. 33,67 The strong complexation of cationic species by the polymer solvating units in such systems results in the formation of longer-lived temporary crosslinks which slow down segmental dynamics. In these systems, increasing salt concentration is inherently at odds with segmental dynamics, and an optimal salt concentration exists for maximum conductivity.…”

Dynamics of supramolecular associative polymer networks at the interplay of chain entanglement, transient chain association, and chain‐sticker clustering

“…A versatile principle for obtaining supramolecular associative polymer networks is through transient linkage of associative side motifs, often named “stickers,” that are distributed randomly along covalently jointed polymer chains . We denote this type of supramolecular associative polymer networks as side‐supra networks .…”

Light‐Controllable Ionic Conductivity in a Polymeric Ionic Liquid

“…10 mol %A GE) with a T g of around À60 8 8Cw as chosen as the PIL precursor. [35,36] First, ascalable and robust synthetic route was developed for DAEs bearing reactive primary amines for attachment to the polymer backbone.F rom the reported DAE-1, N-alkylation of the imidazole unit with N-3-bromopropylphthalimide, followed by methylation with iodomethane,a fforded DAE-3. DAE-BF 4 was produced by deprotection of the phthalimide group and subsequent anion metathesis.AN-hydroxysuccinimidyl (NHS) ester strategy was used to attach the DAE-BF 4 to the PEO-stat-PAGEcopolymer.…”