Role of Chain Polarity on Ion and Polymer Dynamics: Molecular Volume-Based Analysis of the Dielectric Constant for Polymerized Norbornene-Based Ionic Liquids

Abstract

Norbornene-based polymerized ionic liquids (PILs) were systematically prepared to understand the role of PIL architecture and linker on the ionic conductivity (σ DC ), segmental dynamics, and dielectric constant. In PILs with two-or one-armed imidazolium (Im + )-bis(trifluoromethanesulfonyl)imide (Tf 2 N − ) pendants, their dynamics and polarity were tuned by incorporating either oxyethylene [(OCH 2 CH 2 ) x = (OE) x , x = 1 or 3] or alkylene [(CH 2 ) 2 ] moieties as linkers between the norbornene and imidazolium cation moieties and ethyleneoxy [(CH 2 CH 2 O) y = (EO) y , y = 2 or 3] terminal units on the imidazolium. All PILs exhibit three dipolar relaxations; the local chain β motions of the PIL pendants were observed below the glass transition temperature (T g ), while above T g , the segmental α and slower ionic rearranging α 2 relaxations were observed. Unlike the alkylene linker, the OE linker incorporation speeds up the α and α 2 relaxations (consistent with the decrease in T g ), increases the relaxation strengths [leading to an increase in the static and Coulombic dielectric constants (ε s and ε C )], imparts a higher number density of simultaneously conducting ions (p), and boosts their mobility (μ). This is directly reflected in the OE-containing PILs having 10 times higher ionic conductivities (σ DC ) than the PIL with the alkylene linker. The T g , ε s , and σ DC are significantly influenced by the repeat unit molecular volume (V m ), polarizability volume (V p ), and Keesom volume (V K ), suggesting that the OE linker not only facilitates ion dissociation of Im + Tf 2 N − but also promotes segmental motion, thereby leading to a strong correlation of ionic conductivity with the dielectric constant and glass transition temperature.

Electrostatic Manipulation of Phase Behavior in Immiscible Charged Polymer Blends

“…These values give γ ≈ 0.08−0.9 if we assume that l B ≈ 10 nm (a dielectric constant of ϵ ≈ 5.6). We note also that a number of measurements 49,50 of PILs have indicated that very high static dielectric constants (ϵ ≈ 50−100) are possible, which would lower the value of γ further.…”

Ionic Liquid Containing Block Copolymer Dielectrics: Designing for High-Frequency Capacitance, Low-Voltage Operation, and Fast Switching Speeds

“…This placement of the imidazolium moiety was further explored by Kuray et al, who found that materials with the charged moiety placed in a pendant had a greater σ than those with the functionalization directly in the polymer backbone . Choi et al explored the difference in σ between materials with an alkyl spacer versus PEO spacers and showed the PEO-containing PILs were significantly more conductive because of the relatively flexible and polar nature of the PEO spacer that behaves as a plasticizer and solvator. , Other PEO structures have also been explored, such as linear side chain versus cyclic side-chain, as well as utilizing PEO as the polymeric backbone with imidazolium pendant moieties . Ikeda et al explored the length of tail off of the imidazolium pendant and found it has no major influence on T g or conductivity .…”

Ion transport and relaxation in phosphonium poly(ionic liquid) homo‐ and co‐polymers

“…Ultimately, the decoupling of ion dynamics from segmental motion is the most promising approach to achieve high ionic conductivity in polymer electrolytes at room temperature. Moreover, there have been a series of studies to examine the effect of tuning of cation/anion size, 30,31 position of ions (either in the main chain or in the side chain) of PIL, 19,29,32,33 variation of molecular weight, 18 changing the space between neighboring PIL chains, 13 pressure exerted during conductivity measurement, 1 variation of chain length, 34 glass transition temperature ( T g ), 14,30,35 chain polarity, 36 etc., on the change of ionic transport in PIL systems. Dielectric spectroscopic (DS) technique is reported to be the most popular method to investigate ionic conductivity, ion transport and relaxation mechanism in electrolyte systems 29,37–39 .…”