A benzocrown-6-calix[4]arene methacrylate copolymer: Selective extraction of caesium ions from a multi-component system

The synthesis and extraction properties of a copolymer comprised of a 10:1 molar ratio of methyl methacrylate (MMA) and a methacrylate functionalized benzocrown-6-calix[4]arene are reported. Under aqueous-dichloromethane liquid-liquid extraction conditions, the copolymer displayed an enhanced selectivity for caesium over sodium and potassium (in the form of their picrate salts) as compared to an appropriate small molecule analogue. Further, the copolymer was capable of removing caesium nitrate from aqueous solution in the presence of various other anionic (e.g., F^-, Cl^-, and SO₄ ^-) and cationic species (e.g., K⁺ and Na⁺). The ability of this polymeric system to extract inorganic caesium salts into dichloromethane from aqueous media scaled with the relative hydration energies (Δ_hydG°) of each anion studied (i.e., NO₃ ^- > Br^- ≫ Cl^- or F ^-).