Photoinduced Fe-mediated atom transfer radical polymerization in aqueous media

Photoinduced atom transfer radical polymerization with an Fe catalyst was successfully performed in aqueous media for the first time. Three water-soluble ligands [i.e., tetrabutylammonium bromide (TBABr), tris[2-(2-methoxyethoxy)ethyl]amine (TDA), and triphenylphosphine-3,3′,3′′-trisulfonic acid trisodium (TPPSA)] were screened for polymerization in aqueous media. Linear semilogarithmic plots, increasing molecular weights (Mn) with conversion, and low dispersity (Đ < 1.40) were achieved by using a new water-soluble phosphine ligand TPPSA, indicating a well-controlled polymerization. Subsequently, the polymerization kinetics of different catalyst concentrations and the targeted degree of polymerizations were investigated. The applicability of this system to the polymerization of different water-soluble monomers was examined. Furthermore, the polymerization can be regulated by switching the light on and off, which further confirmed its controlled and “living” nature. A successful experiment of chain extension suggested the retention of chain-end functionality. A study of the mechanism showed that the activator (FeIIX2/L) and the additional initiator were generated by the photochemical reduction of FeIIIX3/L in the presence of a monomer. This work provides an environmentally benign ATRP to synthesize well-defined water-soluble materials.