Polymeric Materials for the Separation of f-Elements Utilizing Carbamoylmethylphosphine Oxide Chelating Ligands

The ability of carbamoylmethylphosphine oxide (CMPO) ligands to selectively chelate actinides has been shown to be enhanced by preorganizing the ligands on molecular scaffolds. To increase the preorganization, a new polymeric material with a polyoxanorbornene backbone and CMPO ligand pendant groups has been synthesized, and the ability of the material to selectively extract actinides utilizing a biphasic extraction strategy has been tested. In liquid-liquid extractions of f-block metals from acidic aqueous media into an organic solution containing chelating materials, the polymeric material exhibited a significantly higher ability to extract Th⁴⁺ ions than the monomer, with an order of magnitude greater affinity for the polymeric material in most cases. Due to the unique properties of polymeric materials versus small molecules, additional questions arose as to the effect of molecular weight on extraction efficiency. Extraction and separation efficiencies varied for materials of differing molecular weights, with the largest molecular weight polymer extracting near quantitative amounts of thorium ions, and the smaller molecular weight polymers showing separation factors for Th⁴⁺ ions over Ce³⁺, La³⁺, and Eu³⁺ ions ranging from 124 to 328.