In this paper, an industrial emulsion polymerization process, which is characterized by exothermic reactions with complex nonlinear dynamics, is addressed. In this process vinyl acetate is used as monomer, potassium persulfate as initiator and polyvinyl alcohol as protective colloid. A model of the system to calculate average molecular weight and dispersity is implemented. A fine and strict temperature control is required in order to guarantee the product quality and safe operation. Nonlinear geometric control based on input/output linearization is used for reactor temperature control. An extended Kalman filter is implemented to estimate unmeasured states. Performance tests of the controller and state estimator are carried out by introducing modeling and estimator errors. It is also verified that the nonlinear controller can work with different initiator feed policies helping to improve the process productivity. Finally, compared to a traditional PID controller, the nonlinear geometric controller is superior in rejecting disturbances and performing set point tracking.