In order to describe the influence of a flowing system on the anionic polymerization of E-Caprolactam, a model comprising of classical Malkin kinetics which is embedded in the framework of computational fluid dynamics (CFD) is established and validated with results from different experimental setups, which cover different polymerization temperatures and catalytic systems. As test geometry for a flowing system a plate shaped mold with a single injection point is employed. The main focus of this study lies on fast reactions in order to assess mainly the influence of the flow on the polymerization process and to circumvent any influences of a possible simultaneously happening crystallization. Governed by the flow, local inhomogeneities regarding the polymer conversion arise during the mold filling phase that influence the further course of the reaction and are found to be significant for the entire process far beyond the filling phase. (c) 2014 Elsevier Ltd. All rights reserved.