The kinetics of the soap-free emulsion polymerization of 4-vinylpyridine and styrene, as well as the morphology development during the polymerization, were investigated with H-1-NMR, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. To clarify the process of particle nucleation and particle growth, we focused on the effects of the addition of ethyl acetate (8 wt %) combined with lower rates of agitation (100 and 200 rpm). The results showed that both the nucleation and the growth of particles were related to the monomer droplets stemming from the interface of the monomer and aqueous phases by the disturbance by agitation and/or from the condensation of monomers dissolved in the aqueous phase. Besides the diffusion of monomer molecules through the aqueous phase, the incorporation, among the species previously formed, of monomer droplets was a major cause of monomer transport in the emulsion polymerization system. The particle morphology was controlled by the miscibility of the monomers and (co)polymer, rather than the phase separation due to the different compositions of the copolymers in the particles.