Evolution of iron catalysts for effective living radical polymerization:: Design of phosphine/halogen Ligands in FeX2(PR3)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 PPh3 in the conventional iron catalyst [FeX2(PPh3)(2); X = Cl, Br] improved the catalytic performances such as the activity/controllability. In particular, the butylphosphine bromide derivative [FeBr2(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).