This paper addresses the optimization of a batch copolymerization reactor of styrene and alpha-methylstyrene. The reactor is equipped with a jacket for heat exchange and, thus, for temperature control. The performance index is the batch period, and the decision variable is the jacket inlet temperature. The constraints involved include the process model, the polymer quality, the final monomer conversion rate, the heating/cooling rate of the reactor and upper and lower bounds of the variables. The optimization method is a direct method with a sequential strategy known as control vector parametrization method. The optimal profiles are determined with great care in terms of treatment and fulfilment of constraints. The results show a substantial improvement with respect to the complete discretization method previously used.