A detailed population balance model is developed for the particle-size distribution (PSD) in the emulsion copolymerization of vinyl acetate and butyl acrylate, with nonionic poly(ethylene oxide) surfactants and a redox initiator pair (t-butyl hydrogen peroxide and sodium formaldehyde sulphoxylate). The model accounts for the effects of the nucleation, growth, and coagulation events on the evolution of the PSD. The study addresses the modeling of the coagulation kernel (time-varying and size-dependent intrinsic coagulation rate) under nonionic surfactants. The coagulation-inclusive model results show significant differences front the results generated by a coagulation-free model (even under low solids conditions). More importantly, the coagulation-inclusive model predicts to a reasonable accuracy the experimental data on the full PSD.