The batch emulsion copolymerization of acrylonitrile and butadiene is modeled, with the aim of simulating an industrial process and of improving the final polymer quality. The mathematical model is an extended version of that developed by Gugliotta et al. for a continuous emulsion polymerization of styrene and butadiene. Due to the relatively high solubility of acrylonitrile in water, the following effects are included : (a) the acrylonitrile homopolymerization in the water phase; (b) the desorption of acrylonitrile radicals from the polymer particles; and (c) homogeneous particle nucleation. Apart from simulating two typical batch operations, the model allowed us to develop and simulate a semibatch operation aimed at reducing the copolymer compositional drift. A (suboptimal) semibatch operation was implemented that involved a series of impulsive acrylonitrile additions.