Well controlled nitroxide‐mediated polymerizations of styrene using TEMPO as controller for the production of high molecular weight (MW) polystyrene have been run in a mass‐suspension process at the bench scale using molar ratios of nitroxide (N) to initiator (I) as low as N/I = 0.9. Previously, a kinetic study has been run in bulk polymerization in vials. The two processes show very similar results which demonstrates that the kinetic data collected in bulk can be used to scale‐up the mass‐suspension process. A mathematical model which can emulate the kinetic behavior of both processes has been built. Its kinetic parameters have been mostly taken from the literature and subjected to minimal data fitting using bulk reaction data. Some differences in the outputs of the two processes, especially at low conversions, are explained by the model and ascribed to temperature differences in the two processes.