In this work, attention is focused on two on-line optimization strategies for a batch MMA polymerization process, based on a physical process model and temperature measurements. Several model uncertainties are considered, including the variation of the heat transfer coefficient between the cooling jacket and the reactor medium as well as unknown parameters in the description of the gel effect. The first strategy is based on a worst-case analysis (formulated as a min-max problem), leading to an open-loop control scheme. The possibility to combine this scheme with a feedback controller is also evaluated. The second strategy is based on a scheduled optimization approach, i.e., the model parameters are periodically re-estimated on-line, and optimal trajectories are re-evaluated. (c) 2006 Elsevier Ltd. All rights reserved.