An experimental and theoretical study has been carried out for on-line estimation and control of a batch reactor for solution polymerization of methyl methacrylate. The main control objective is to bring the reactor temperature to its target temperature as rapidly as possible with minimal temperature overshoot. The extended Kalman filter algorithm is used to estimate the effective reactor wall heat transfer coefficient, which is used to calculate a jacket set point automatically for a cascade control. Control performance for the proposed method is compared to that of a conventional PID controller. It has been observed that temperature overshoot can be minimized by the proposed method with the use of both reactor and jacket energy balances for reactor temperature control. When direct measurements of monomer conversion are not available, the extended Kalman filter is also used to estimate the rate of heat generated by poly-merization which is integrated to obtain an estimate of monomer conversion. It is observed that the model and measurement error covariance values, which are essentially the filter tuning parameters, strongly influence the accuracy of resulting monomer conversion estimates.