Phosphine–Ligand Decoration toward Active and Robust Iron Catalysts in LRP

Abstract

Phosphine ligands were designed to enhance the catalytic activity of iron(II) complexes [FeBr2(PR3)2] for metal-catalyzed living radical polymerization (LRP), and special efforts were directed to the improvement in catalytic activity and robustness against functional monomers. Introduction of an electron donating group {methoxy [P(MeOPh)3] or N,N′-dimethylamino [Ph2P(Me2NPh)]} onto the para position of triphenyl phosphine (PPh3) allowed active and robust Fe(II) complexes that catalyzed LRP of poly(ethylene glycol) methacrylate (PEGMA) smoothly proceeding to high conversion (∼90%), to form polymers of controlled molecular weights and its distributions (Mw/Mn < 1.2). In contrast, such an enhancement was absent with the parent ligand PPh3 and those with electron-withdrawing substituents. Furthermore, the replacement of the three methoxy groups in P(MeOPh)3 with PEG chains led to a more robust catalyst, especially tolerant of the hydroxyl group in 2-hydroxyethyl methacrylate (HEMA). Accordingly, this catalyst enabled a four-component random living copolymerization of HEMA, PEGMA, and two alkyl methacrylates, where all the monomers randomly copolymerized into statistical copolymers of controlled molecular weights.