The importance of diffusional limitations in controlled radical polymerization at laboratory scale and in homogeneous medium is highlighted using different diffusion models. In particular, a coupled 'parallel' encounter pair model is introduced which allows a rigorous description of the influence of diffusional limitations on the activation/deactivation process. Diffusional limitations on termination have a significant influence, whereas those on the activation/deactivation process can disturb the regular growth pattern at high conversion if the mediating agent is a sufficiently bulky species. Diffusional limitations on initiation are only important in case radical initiator is still present at high conversion
