Synthesis and Performance of Aromatic Polyamide Ionenes as Gas Separation Membranes

Here, we report the synthesis and thermophysical properties of seven primarily aromatic, imidazolium-based polyamide ionenes. The effects of varied para-, meta-, and ortho-connectivity, and spacing of ionic and amide functional groups, on structural and thermophysical properties were analyzed. Suitable, robust derivatives were cast into thin films, neat, or with stoichiometric equivalents of the ionic liquid (IL) 1-benzy-3-methylimidazolium bistriflimide ([Bnmim][Tf₂N]), and the gas transport properties of these membranes were measured. Pure gas permeabilities and permselectivities for N₂, CH₄, and CO₂ are reported. Consistent para-connectivity in the backbone was shown to yield the highest CO₂ permeability and suitability for casting as a very thin, flexible film. Derivatives containing terephthalamide segments exhibited the highest CO₂/CH₄ and CO₂/N₂ selectivities, yet CO₂ permeability decreased with further deviation from consistent para-linkages.