A moving-horizon inferential-state estimation technique is described which uses simulated "experimental" data on temperature and viscosity to study bulk polymerization of free-radical systems. The short-term predictive capability of this technique is found to be quite good. A considerable amount of ringing (oscillations between the lower and upper bounds) is observed in the values of the estimated parameters which can be reduced significantly by narrowing down the range of parameter values or by including longer horizons in parameter estimation. Short-range prediction of viscosity was also found to be good. The model-calculated values of monomer conversion and molecular weights were found to be quite satisfactory in the entire range of operation. The long-term predictions of the model using the estimated parameters may or may not be accurate depending on the length of historical data used in the prediction. However, periodic use of state-variable estimation based on all the data up to that time, followed by the determination of the optimal temperature history in the future, could be a feasible strategy for experimental on-line optimizing control of bulk free-radical polymerizations which exhibit significant amounts of the Trommsdorff effect.