Mechanism of Ion Transport in Imidazolium Polymerized Ionic Liquids (PILs) Bearing a Polythiophene Backbone and in Dual Ionic Conductors of Polyfluorene Block Copolymers Doped with LiTFSI.

Understanding the mechanism of ion transport in polyelectrolytes based on Polymerized Ionic Liquids (PILs) is of great importance for increasing the RT conductivity. Herein, imidazolium PILs bearing a polythiophene backbone with four different N-alkyl side-chain lengths and seven different counteranions were synthesized and investigated with respect to the ion conduction. Cation-anion complexation strongly influences the backbone dynamics and the associated dc-conductivity. Ionic conductivity measurements as a function of pressure revealed that ion motion is facilitated by local anion jumps with a length scale on the order of the charge alternation distance. A simple “stick and jump” model can account for the increased backbone mobility and the concomitant enhanced ion conductivity for anions with intermediate size ([TFSI]^-).
In the second part, dual ionic conductors of polyfluorene block copolymers consisting of blocks with side groups bearing imidazolium PIL with a [Br]^- counteranion and blocks with EO side groups doped with LiTFSI were investigated with respect to the ion transport. Ionic conductivity measurements as a function of pressure revealed that in these dual ion conductors ([Br]^- vs [LiTFSI]^-) it is the hopping of Li ions that controls the conduction process.