The effect of initial ligand concentration on the apparent rate constant of propagation of single-electron transfer living radical polymerization (SET-LRP) of MA in DMSO at 25 degrees C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate-order for the ligand concentration could be determined. Rather, the response of the rate of SET-LRP to initial ligand concentration is complex and is likely determined by a competition of ligand-dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET-LRP. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5629-5638, 2009