Polymeric Ionic Liquids: Comparison of Polycations and Polyanions

The achievement of high ionic conductivity in new “polymeric ionic liquids” (PILs) is of great interest as it refers to the solid state electrolytes and their applications in electrochemistry. Four ionic monomers, including two new ones, namely N-[(2-methacryloyloxy)-propyl]-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (M1), 1-[2-(methacryloyloxy)propyl]-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (M2), N-methyl-N-ethylpyrrolidinium(3-sulfopropyl) methacrylate (M3), and 1-methyl-3-ethylimidazolium(3-sulfopropyl) methacrylate (M4), were prepared and used both for the synthesis of linear PILs and ionic networks with poly(ethylene glycol) dimethacrylate (PEGDM). The optimal polymerization conditions for obtaining high molar mass PILs (M sD up to 1.24 × 106 g/mol) were identified. The copolymerization of oppositely charged monomers was studied as well. Polycations, polyanions, and their random ionic copolymers were compared in terms of their physical properties. The examined properties were found to depend mainly on the nature of the counterion. It became obvious that the bulk ionic conductivity of hydrophilic polyanions is greatly affected by the humidity. It increases up to 220 times upon transferring from dry air to 20% relative humidity. Ionic conductivity increased in random ionic copolymers synthesized from oppositely charged monomers feasibly, suggesting that the ion transport was improved by the partial formation of mobile ionic liquid within the polymer.