Effect of [Pyridylmethanimine]/[Cu I ] Ratio, Ligand, Solvent and Temperature on the Activation Rate Constants in Atom Transfer Radical Polymerization

Summary: The effect of [L]/[Cu I ] ratio, ligand, the choice of solvent and temperature on the activation rate constants in ATRP with catalyst complexes formed with two pyridylmethanimine ligands [PMI, i.e., N ‐propyl‐pyridylmethanimine (NPPMI) and N ‐octyl‐pyridylmethanimine (NOPMI)] were studied. Maximal values for the apparent rate constants were observed at an [L]/[Cu I ] ratio of ∼2/1 and 1/1 in polar and nonpolar solvents, respectively. This is similar to the results obtained with the Cu I /bpy system and was attributed to the formation of [Cu I /L 2 ] + Br − and [Cu I /L 2 ] + Cu I Br   2 −species. The Cu I /NPPMI system was only soluble in polar reaction media; however, the Cu I /NOPMI complex was soluble in both polar and less polar reaction media. The activation rate constants increased with increasing temperature and the value of activation energy ( E a ) for Cu I /NPPMI in the activation process was 58.1 kJ ·  M −1  · K −1 .Arrhenius plot of ln k a versus 1/ T for the activation process for NPPMI and bpy in acetonitrile; [Cu I Br/NPPMI 2 ] 0 ([Cu I Br/bpy 2 ] 0 )/[EtBriB] 0 /[TEMPO] 0 /[TCB] 0  = 20/1/10/2 × 10 −3 M .