The automation and control of polymerization reactors that operate in batches is quite a difficult task. The gel effect and the absence of a stable operational state are factors that determine the need for special control systems. In this study, a methodology is implemented for controlling the operation of a batch polymerization reactor, utilizing an adaptive controller of the type STC (Self Tuning Controller). By utilizing a model of the polymerization process, the necessary operational conditions were determined for producing the polymer within the desired characteristics. Variables of the mean molecular weight type and the polydispersion rate were utilized as polymer quality parameters. Experimental tests in a pilot unit of polystyrene production in suspension, showed the capacity of the STC for controlling this type of reactor. The results also showed that, from the methodology utilized for determining the operational variables, polymers with previously defined characteristics can be produced.