Temperature-Driven Recycling of a Bioderived Iron Catalyst for Aqueous Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) offers precise control over macromolecular structure but typically relies on copper catalysts with limited recyclability, high cost, and poor biocompatibility. To provide a more sustainable alternative, we developed oHemin, a protein-inspired iron catalyst obtained in a one-pot, quantitative synthesis. Its hemin core is surrounded by thermoresponsive poly(ethylene glycol methacrylate) oligomers, which impart water solubility and allow simple recovery via temperature-induced separation. The oHemin catalyst enabled well-controlled ATRP of water-soluble methacrylates in aqueous media at 30°C, yielding polymers with dispersities as low as 1.3, and could be readily separated and recycled multiple times by heating to 60 °C without loss of activity. The catalyst was compatible with neutral, anionic, cationic, and zwitterionic water-soluble monomers. Mechanistic studies confirmed that the iron center was accessible for alkyl halide activation, halide anion binding, and radical deactivation, ensuring controlled polymerization.