Preparation and Characterization of Ionic Liquid Copolymers for Lithium Ion Conduction

Ionic liquids, molten salts at room temperature, have been expected as novel ion conductive materials owing to their unique characteristics such as non-volatility and excellent ionic conductivity. However the component ions of ionic liquid migrate with target ions along with potential gradient. To improve this drawback, we had proposed zwitterionic liquids in which component cation and anion were tethered by spacer. On the other hand, ionic liquid polymers were also effective for target ion conduction, in which ionic liquid component ions were tethered on the polymer main chain. In particular, copolymerization of ionic liquids provides target ion conductive polymer films were suggested. In this work, we prepared and characterized ionic liquid copolymers to achieve fast conduction of target ions. Cationic monomer An, which has hydrocarbon spacer between polymerizable group and ionic liquid moiety. Anionic monomer Bm having benzene sulfonic acid lithium salt on polyether chain end. Structure of two kinds of monomer is shown in Scheme 1. The monomers were mixed with suitable composition and polymerized with AIBN as initiator at 70 C in the bulk. No unreacted monomer was confirmed by using FT-IR. Obtained polymers were dried in vacuo at 80 C and then characterized by complex impedance measurement, DSC, TG/DTA and direct-current polarization method.