Reducing the reducing agent concentration further to 1 mM yielded even thicker brushes, indicating that we are still in the regime of 'overly fast ATRP'. However, when the reducing agent concentration was again cut in half to 0.5 mM, brushes with inconsistent thicknesses and large edge gradients were obtained. Likely, 0.5 mM of ascorbic acid does not provide sufficient oxygen tolerance, making the process too susceptible to small variations in oxygen ingress, and thereby yielding inconsistent results. Therefore, ARGET-ATRP in this configuration presents a trade-off between oxygen tolerance and polymerization control; in contrast to ATRP performed under anaerobic conditions, lowering the reducing agent concentration does not per se lead to better control over thickness. The results of the kinetic study for several reducing agent concentrations are shown in Figure .