Exploration of highly active bidentate ligands for iron (III)-catalyzed ATRP

Novel highly active substituted P-N ligands were found to be remarkably efficient for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and butyl methacrylate (BMA). The reaction was catalyzed by a high oxidation state metal (FeX₃) coupled with ethyl-2-bromoisobutyrate (EBriB) as an ATRP initiator. MMA polymerization was examined by the gradual addition of FeX₃ and the complete transformation of uncontrolled ATRP (PDI∼1.59) to a controlled polymerization system (PDI∼1.13) was observed. The polymerizations were well controlled with a linear increase in the mean molecular weight (M_n) and monomer conversion reached up to 90% without complications. In the case of the DTBP ligand, the experimental molecular weights matched the theoretical values well and the PDIs were narrower (<1.2) compared to the other ligands. Furthermore, the potentially active catalyst (FeBr₃/DTBP) was used successfully for the polymerization of MMA at a 50-ppm catalyst loading. The probable mechanism using FeX₃ without an external additive was also determined.