Dielectric relaxation behavior of polymerized ionic liquids with various charge densities

The dielectric relaxation of polymerized ionic liquids with various charge densities was investigated in order to understand the effects of charged units and counterions on the microdynamics of solid state polyelectrolytes. Copolymers of poly(1-vinyimidazole-ran-1-ethyl-3-vinylimidazolium bis(trifluoromethane)sulfonylimide) (P(VI/C2TFSI)) with a various degree of ionic content (corresponding to C2TFSI units), xq, were synthesized, to create copolymer segments with ionic and electrically neutral units. P(VI/C2TFSI) showed three dielectric relaxation modes: side-chain motion, ion-pair motion and polymer segmental motion. Ion-pair relaxation times strongly correlated with specific electric conductivity irrespective of xq, and showed Arrhenius-type temperature dependence below the glass transition temperature, and Vogel-Fulcher-Tamman-type temperature dependence above the glass transition temperature. The specific electric conductivity of the fragile Arrhenius component is a minor contribution in P(VI/C2TFSI) with xq ≤ 0.09, in contrast with high xq copolymers. Counterion dissociation becomes restricted in P(VI/C2TFSI) with xq ≥ 0.46, which is interpreted as the counterion condensation that is typically observed in aqueous polyelectrolyte systems.