In nitroxide-mediated polymerizations, control of the reaction is provided by
reversible capping and de-capping of the growing (radical) polymer chain by a nitroxide
radical. As a result, the concentration of the growing radical species is decreased and the
speed of the polymerization is significantly decelerated. Consequently, the polymer
chains grow with a (quasi) uniform speed, and side reactions, like the bimolecular
termination, are kept at a minimum. Consequently, the polymers show relatively narrow
molecular weight distributions. In order to gain optimum control over the radical
polymerization, one-component species (decomposing into an initiating radical and a
nitroxide radical) have shown to be superior to two-component mixtures, as the latter
exhibit the disadvantage of inaccurately specified efficiencies of the initiating radical