Fe(iii)-mediated ICAR ATRP in a p-xylene/PEG-200 biphasic system: facile and highly efficient separation and recycling of an iron catalyst

Abstract

Iron catalysts are attractive catalysts for atom transfer radical polymerization (ATRP) owing to their abundancy, low toxicity and good biocompatibility. However, the recycling of iron catalysts is still a great challenge although the recycling of copper catalysts has achieved success. In this work, we develop a facile and highly efficient separation and recycling strategy for an iron catalyst combining thermoregulated phase separable catalysis (TPSC) and initiators for continuous activator regeneration for atom transfer radical polymerization (ICAR ATRP) in a PEG-200/p-xylene biphasic system. Herein, FeCl₃·6H₂O was used as the catalyst, tetrabutylammonium bromide (TBABr) as the ligand, 2,2′-azobisisobutyronitrile (AIBN) as the reducing agent, ethyl-2-bromo-2-phenyl acetate (EBPA) as the initiator, and methyl methacrylate (MMA) as the model monomer. The PEG-200/p-xylene biphasic system formed a homogeneous polymerization solution at 70 °C, and the iron catalyst could be easily separated in situ just by a simple standing and decantation process, and was therefore recycled for the next polymerization when the polymerization temperature decreased to room temperature. In this novel polymerization system, well-defined PMMA with controlled molecular weights and narrow molecular weight distributions could be easily obtained, and the iron catalyst could be recycled in situ 10 times without any significant loss of the catalyst activity. In addition, this novel strategy was also extended to other hydrophobic monomers such as styrene, methyl acrylate and tert-butyl acrylate, indicating a versatile method for iron catalysis, separation and recycling.