Ion-conductive polymer membranes containing 1-butyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethylimidazolium trifluoromethanesulfonate

Membranes were prepared by casting a solution of a polymer and ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO] or 1-ethylimidazolium trifluoromethanesulfonate [EIM][TfO] typical representatives of aprotic and protic ionic liquid and evaporating the solvent. The following polymers were used: Udel-type polysulfone, polybenzimidazole derivative containing benzofuranone moieties (PBI-O-Ph), poly(vinylidene fluoride-co-hexafluoropropene) (fluoroelastomer) and Nafion. Polymer–ionic liquid compatibility was investigated by swelling, scanning electron microscopy and differential scanning calorimetry. Membranes conductivities in anhydrous atmosphere depended on temperature, ionic liquid concentration in the membrane, and on the type of matrix polymer. No conductivity could be detected with polysulfone-based membranes due to the incompatibility of polysulfone and the two ionic liquids, low conductivities were found with PBI-O-Ph based membranes, the conductivities of the fully compatible systems based on fluoroelastomer or Nafion matrixes amounted to 40% of that of neat ionic liquids.

Research highlights▶ Polymer membranes based on ionic liquids [BMIM][TfO] or [EIM][TfO] prepared. ▶ Two very similar ionic liquids – one being aprotic and the other protic. ▶ Similar affinity to polymers and similar ionic conductivity in polymer membranes.