Polymers with multiple ligand sites for metal extractions in dense-phase carbon dioxide

We have synthesized a series of CO₂-soluble polymeric extractants with multiple ligand sites for CO₂-based metal extractions. The CO₂-soluble polymers were prepared via free-radical copolymerization of a fluorinated acrylate with a series of acrylate- or styrene-based monomers functionalized with ligand sites or ligand precursors. These polymers have high solubility in CO₂; up to 30 wt % of a polymer with 15 mol % of a ligand-based monomer can be solubilized in liquid CO₂ at 25°C at 140 bar. Copper and europium extractions have been performed with β-diketone- and phosphonate-functionalized polymers, respectively. Preliminary extractions with copper nitrate were carried out at ligand-to-metal ratios of 1:1 and 2.7:1, resulting in 25-37% and 59% efficiency, respectively, suggesting a ligand binding stoichiometry of 2 for efficient extraction. Europium luminescence studies demonstrate that europium is bound to the polymer along with four water molecules in the inner coordination sphere.