Low ppm CuBr-Triggered Atom Transfer Radical Polymerization under Mild Conditions

Conventional atom transfer radical polymerization, also referred to as traditional or normal ATRP, typically operates in the presence of large amounts of a CuBr activator and at relatively high temperatures (>60 °C). In this work, we report that ppm concentrations of CuBr are capable of triggering an efficient ATRP reaction at ambient temperature. In the presence of an excess ligand and the absence of any external CuBr2 deactivator, narrow molecular weight distributions can be achieved, even at quantitative monomer conversions (as low as 1.05 at >99% conversion). High end-group fidelity was demonstrated by matrix-assisted laser desorption/ionization time of flight mass spectrometry and further exemplified by in situ chain extensions upon sequential monomer addition, furnishing well-defined diblock copolymers with equally low dispersities. Although dimethylsulfoxide was found to be the most efficient solvent, methanol, trifluoroethanol, N,N-dimethylformamide, and acetonitrile could also be employed, showing good control over the polymerization, albeit exhibiting slower polymerization rates. Detailed UV-vis measurements in a range of solvents in conjunction with polymerization experiments starting with CuBr2/Me6TREN show reduction of CuBr2 under the conditions employed, suggesting a hybrid mechanism of ARGET and conventional ATRP.