With ammonium persulphate as initiator and Aerosol MA and Aerosol OT as emulsifiers, batch copolymerization of butyl acrylate and vinyl acetate (VAc) was investigated at 60 ยฐ, varying only the initial monomer feed composition. Accurate kinetic (polymerization rates, sequence distribution) and colloidal data (particle size and distribution) were collected on the final latexes and as a function of conversion. Polymerization in the water phase was not negligible for VAc and experimental data were well fitted by simulations taking into account the monomer partition between water and organic phases. Moreover, the simulation of the particle monomer swelling makes possible determination of the overall propagation rate constant, its changes as a function of conversion and, as a consequence, to derive from kinetic (Rp) and colloidal (N o) data, the changes in the average number of radicals per particle, a. The lower polymerization rates observed for copolymerizations, by comparison with the homopolymerizations, can be explained in terms of a change in the overall propagation rate constant as well as in ~i. Experimental data and theoretical simulations, which fit quite well, are in agreement with homogeneous particle nucleation mechanisms and particle structuration.