Three calix [4]crown-4 derivatives and their oligomers, p-tert-butylcalix [4]crown-4 oligomer 5, p-tert-butylcalix [4]dioxacrown-4 oligomer 6, p-tert-butylcalix [4]diazacrown-4 oligomer 7 that contain hard and soft ion binding sites, are synthesized to estimate selective extraction of cesium ions from the aqueous to the organic phase. The binding sites may complex alkali metal ions or transition metal ions selectively. Oligomers are fairly good extractants for transition metal ions in comparison with their monomers, which suggests that polyoxyethylene bridges are efficient for complexing metal ions, especially for transition metal ions. (c) 2007 Wiley Periodicals, Inc.