A novel control system for semibatch polymerization reactors based on nonlinear MPC is proposed that is aimed to deal with more than one control objective. Commonly, multi-objective control problems are reduced to single objective problems, but better control can be achieved by solving the problem as a true multi-objective optimization problem because the interactions among the control goals are taken into account. Moreover, the selection of subjective weighting functions is avoided. The procedure is based on computing a trade-off solution among the control objectives that features the minimum distance from a given point on the Pareto front to the Utopia region. To illustrate the application of the multi-objective nonlinear MPC strategy two complex reaction systems are deployed.