Local Chain Dynamics in Sequence-Controlled Polymers as a Tunable Handle for Rare Earth Sequestration

Chain dynamics govern the intricate behaviors of proteins, underpinning functions such as catalysis, recognition and stimulus response, and are an increasingly appreciated aspect of structure-function relationships. Analogously, manipulating chain dynamics and structure in abiotic polymers via sequence control is an exciting, yet underexplored, strategy for improving material functions. Here, we report a systematic study relating the sequence, structure, and dynamics of polymeric sequestrants to their binding affinity and selectivity for rare earth elements (REEs). A series of sequence-controlled polymers with metal chelating, solubilizing, and structure forming monomers was synthesized via multiblock polymerization, yielding compositionally identical polymers with spectroscopically resolved domains and distinct morphologies. Using a combination of small angle X-ray scattering and 19F NMR relaxometry measurements, we connected differences in polymer structure and dynamics to polymer sequence variables such as the patchiness (density) of the structure forming monomer and the location of the chelating monomer. Furthermore, we found that while all polymers in the series collapse more and have slower dynamics when binding REEs (lanthanum and lutetium) than calcium, these changes were sequence-dependent and localized to specific domains within the polymer. Notably, sequence-controlled polymers that exhibited the largest conformational and dynamic changes upon binding REEs also bound REEs with the greatest affinity and moderate selectivity. Collectively, these results establish a mechanistic link between monomer patterning, dynamics, morphology, and REE binding performance en route to the development of efficient and selective macromolecular chelators.