This work reports the development of a simulation model for batch, semibatch, or continuous emulsion polymerization of styrene under nonisothermal conditions. We demonstrate the use of the model to explore methods for controlling the particle size distribution. Sensitivity results suggest that accurate identification of model parameters from online data requires operation in semibatch rather than purely batch mode. The extensions to the nonisothermal case represent a significant step forward in the development of recipes for batch or semibatch polymerization in which temperature can be manipulated to achieve final product specifications. Our model is based on the zero-one population balance model of Coen et al. (Polymer 1998, 39, 7099-7112) extended to the nonisothermal, semibatch case. The model will be used for control studies and as a step toward online model-based control of semibatch polymerization reactors.