Effect of [PMDETA]/[Cu(I)] Ratio, Monomer, Solvent, Counterion, Ligand, and Alkyl Bromide on the Activation Rate Constants in Atom Transfer Radical Polymerization

A detailed study on the effect of [PMDETA]/[Cu(I)] ratio, monomer, solvent polarity, counterion, ligand, and alkyl bromide on the activation rate constant ( k act ) in ATRP was carried out. The highest values of k act for Cu(I)Br were obtained at [PMDETA]/[Cu(I)Br] ∼ 1/1 in more polar solvents and ascribed to a neutral [Cu(PMDETA)Br] structure of the complex. However, in less polar solvent mixtures a relatively fast reaction was observed already at the 0.5/1 ratio with the smaller rate increase up to [PMDETA]/[Cu(I)Br] ∼ 1/1. The highest values of k act for Cu(I)PF 6 were observed at [PMDETA]/[Cu(I)Br] ∼ 1/1 in more polar, less polar solvent mixtures and monomer, which was explained by the formation of an ionic [Cu(PMDETA)] + PF 6 - complex. In both more polar and less polar media, the values of k act were slightely larger for PF 6 - than Br - counterion. However, in methyl acrylate, k act was 1.9 times larger for Br - than PF 6 - counterion. This was attributed to monomer coordination through the open coordination site of an ionic [Cu(PMDETA)] + Y - (Y = PF 6 /BPh 4 ) complex, which reduced complex activity. The values of k act were higher for PMDETA containing three nitrogen atoms as compared to the ligand containing two nitrogen atoms and one oxygen atom (BDMAEE). The relative rates of k act of the alkyl bromides follow the order EBriB (30) ≫ MBrP (3) > t-BBrP (1). In the absence of monomer, the values of the k act for different ligand/counterion follow the order PMDETA/PF 6 - > PMDETA/Br - > BDMAEE/Br - > bpy/PF 6 - > bpy/Br - .