Synthesis of imidazolium-based poly(ionic liquid)s and their application to ion-exchange materials

Linear and networked poly(ionic liquid)s, which were composed of polyoxetanes and imidazolium groups, were synthesized by cationic polymerization of mono- and di- functional oxetanyl monomers, and the properties of the obtained polymers were investigated. The monofunctional monomer, 3-(3-ethyl-3-oxetanylmethyl)-1,2-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (OXDMImTFSI), was prepared from the reaction of 3-ethyl-3-oxetanylmethyl chloride with 1,2-dimethylimidazole followed by exchanging the chloride to bis(trifluonomethanesulfonyl)imide (TFSI). The difunctional monomer, 1,3-di(3-ethyl-3-oxetanylmethyl)-2-methylimidazolium bis(trifluoromethanesulfonyl)imide (DOXMImTFSI), was prepared from the reaction of 3-ethyl-3-oxetanylmethyl chloride with 2-methylimidazole and successive ion-exchange of chloride to TFSI. OXDMImTFSI was polymerized by addition of a catalytic amount of BF3 diethyl ether complex. The obtained linear polyOXDMImTFSI showed good stability toward heat and basic conditions. Networked polymer films were prepared by homo/co-polymerization of DOXMImTFSI or DOXMImTFSI/OXDMImTFSI liquid layers using the thermally latent cationic initiator, (1-naphthylmethyl) methyl p-hydroxyphenyl sulfonium hexafluoroantimonate (SI-60). The obtained films showed good ion-exchange ability between TFSI, Cl, and OH anions.