To probe the influence of structural variation within dibenzo-16-crown-5-oxyacetic acids upon the selectivity of alkali metal cation separations by solvent extraction and liquid membrane transport processes, studies have now been conducted in homogeneous solution by NMR spectroscopy and titration calorimetry and in the solid state. Condensation polymerization of such proton-ionizable lariat ethers with formaldehyde produces a new class of ion-exchange resins which contain cyclic polyether binding sites as well as ion-exchange site for metal ion complexation.