Evolution of Iron Catalysts for Effective Living Radical Polymerization: Design of Phosphine/Halogen Ligands in FeX 2 (PR 3 ) 2

In this article, we report the evolved system of iron-complex-catalyzed living radical polymerization of methyl methacrylate (MMA), through design of the ligand, combination of the halogen in the initiator/catalyst, and optimization of the polymerization conditions, toward improvement of the activity and the polymerization-controllability with the applicable catalysts. Introduction of the more basic ligands such as PMe(Ph) 2 and P- n -Bu 3 in place of PPh 3 in the conventional iron catalyst [FeX 2 (PPh 3 ) 2; X = Cl, Br] improved the catalytic performances such as the activity/controllability. In particular, the butylphosphine bromide derivative [FeBr 2 (P- n -Bu 3 ) 2 ] in conjunction with a bromide initiator [(MMA) 2 Br] allowed a faster and more precise polymerization, where the conversion reached over 90% without serious deactivation and the molecular weights and their distributions of the obtained PMMAs were fairly controlled ( M w / M n = 1.2−1.3). The high efficiency of the system was demonstrated by the successful monomer-addition experiment and block copolymerization with buthyl methacrylate (BMA).