This paper discusses a method to improve the quality of temperature control of the polyvinyl chloride (PVC) emulsion reactor by implementing Model Predictive Control (MPC) and cascade control for this exponentially unstable process with very non-linear behaviour. These methods were tested for different disturbances, and their performances were compared with those obtained with classical proportional-integral-derivative (PID) control. Significant improvement of temperature control was achieved using MPC. The process model used in MPC is presented.