The atom transfer radical polymerization of [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) has been studied under different [Cu-I]/[Cu-II] ratios. The reaction kinetics is followed by ellipsometry and quartz crystal microbalance and it was found that the reaction speed influences the grafting density of the polymer brushes. High [Cu-I]/[Cu-II] ratios, i.e., fast polymerizations, lead to less dense polymer brushes.