A common problem in emulsion polymerization reactors is to maximize the production under safe conditions of copolymers of the desired composition. This is a difficult task because of the lack of accurate models for the process. In this work this problem is solved by using a hierarchical fuzzy-logic model-based controller. The fuzzy system was used for planning and its role was to determine the optimal trajectory. A model-based controller was used to track this trajectory. The controller performance was checked by simulation of the emulsion polymerization of styrene and butyl acrylate carried out in a 15 m(3) reactor.