Ion specific, odd–even glass transition temperatures and conductivities in precise network polymerized ionic liquids†
A series of crosslinked network polymerized ionic liquids (n-PILs) were synthesized with precise linker lengths, ranging from 4–12 carbons, to investigate the role of network nanostructure and electrostatic interactions on ion transport. The n-PILs contain tethered ammonium cations and either spherical BF4 or large, non-spherical bis(trifluoromethane)sulfonimide (TFSI) mobile anions. In the TFSI networks, a pronounced odd–even effect is observed with carbon linker length where the glass transition temperature (Tg) can vary by 45 K and conductivity by almost two orders of magnitude simply by adding one carbon between the junctions. The dynamic fragility of the temperature-dependent conductivity also shows an odd–even effect. In the BF4 networks, made from the same initial network, higher Tgs are observed with no odd–even effect. Both versions of the networks exhibit ionic aggregation peaks (via wide-angle X-ray scattering) which show monotonic variations with carbon length. These findings indicate that major odd–even Tg and conductivity effects can be observed with small variations in the chemical structure.
- This article is part of the themed collection: Charge Transporting Nanostructured Polymers for Electrochemical Systems