Investigating the Influence of Chain Density on Lanthanide Binding within Star Copolymers

Rare earth elements (lanthanides) are critical to modern technologies, yet their similar physicochemical properties make separation and purification challenging. Conventional solvent-based methods are inefficient and generate hazardous waste, motivating the development of more selective and sustainable approaches. Metal-chelating polymers offer a promising alternative by forming hydrophobic binding pockets that mimic protein environments and enable reusable, high-affinity materials. This work investigates star copolymer single-chain nanoparticles (SCNPs), which exhibit increased core chain density, enhancing chelating group proximity and local hydrophobicity to improve lanthanide binding. Linear, 2-arm, and 4-arm architectures were synthesized to systematically tune hydrophobic microenvironments through chain and hydrophobic block densities. The generation of these microenvironments promotes entropically driven metal binding through water release. Binding affinities were quantified using a xylenol orange competitive dye assay. Increased block hydrophobicity strongly enhanced metal binding, with star architectures outperforming linear analogues. These results establish design principles for polymer-based sequestrants to improve the efficiency and scalability of lanthanide recycling.