Facile, simple, and inexpensive ionic liquid, 1-phenyl-3-methylimidazole diphenyl phosphate, as an efficient phosphorus-based ligand for copper-catalyzed reverse atom transfer radical polymerization of methyl methacrylate

Abstract

Ligands play a vital role in atom transfer radical polymerization (ATRP) in solubilizing the transition-metal salt and adjusting the redox potential of the metal center. In general, nitrogen ligands work particularly well for copper-mediated ATRP, while phosphorus-based ligands are rarely used due to less effectiveness. Therefore, this work aims to explore for the first time a facile, simple, and inexpensive ionic liquid (IL), 1-phenyl-3-methylimidazole diphenyl phosphate ([Phmim][Ph₂PO₄]), as an efficient phosphorus ligand for CuBr₂-mediated reverse ATRP. The key to success is ascribed to stronger complexation of the IL ligand with the catalyst and higher solubility of the resulting complex. The polymerizations proceeded in a controlled/“living” fashion, as evidenced by first-order kinetics, linear evolution of molecular weights with monomer conversion, and narrow molecular weight distributions. Effects of various experimental parameters—solvent, reaction temperature, IL, and molar ratio of CuBr₂/[Phmim][Ph₂PO₄]—on the polymerization were investigated in detail. Furthermore, ¹H NMR analysis confirmed the halogen-containing chain-end functionality of the resultant polymer.