Viscoelastic Behavior of Polymerized Ionic Liquids with Various Charge Densities

抄録

The viscoelastic behavior of polymerized ionic liquids made up of poly(1-vinylimidazole-ran-1-ethyl-3-vinylimidazolium bis(trifluoromethane)sulfonylimide) (P(VI/C₂TFSI)) with varying degrees of quarternization (χ_q) was investigated to understand the relationship between macro physical properties and the charge density of polymer chains. The time-temperature superposition principle was found to be valid for P(VI/C₂TFSI) irrespective of χ_q value and yielded a universal master curve. The terminal response times decreased with increasing χ_q due to the dilution of polymer chains caused by the increasing TFSI^- concentration. Master curves of P(VI/C₂TFSI) with high χ_q showed broad shoulders in the glass-to-rubber transition region, which reflected either rotational motion of TFSI^- or sub-Rouse motion of the polymer chains. The fragility index decreased with increasing χ_q, indicating that the polymerized ionic liquids were less fragile in comparison with the ionomers or electrically neutral polymers. By observing the change in the fragility index, the transition between ionomers and polymerized ionic liquids was determined to be χ_q = 0.10 ∼ 0.25.