Effects of ethyl acetate on the soap-free emulsion polymerization of 4-vinylpyridine and styrene. II. Aspects of the mechanism

The kinetics of the soap-free emulsion polymerization of 4-vinylpyridine an d 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 effe cts 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 an d the growth of particles were related to the monomer droplets stemming fro m the interface of the monomer and aqueous phases by the disturbance by agi tation and/or from the condensation of monomers dissolved in the aqueous ph ase. 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 syst em. The particle morphology was controlled by the miscibility of the monome rs and (co)polymer, rather than the phase separation due to the different c ompositions of the copolymers in the particles. (C) 2001 John Wiley & Sons, Inc.