EQUILIBRIUM ENCAPSULATION OF POLYSTYRENE LATEX PARTICLES

The authors have performed a series of seeded styrene emulsion polymerizations in which the second stage of growth was initiated only after the second-stage monomer charge had achieved equilibrium saturation with the seed particles. The final particles were observed in the electron microscope by using two means of distinguishing between the first- and second-generation polymer: butadiene tagging and osmium tetroxide staining coupled with ultramicrotomy and tritiated-styrene tagging coupled with autoradiographic detection. It is found that the first- and second-generation polymer chains are not uniformly mixed throughout the final latex product; rather, the second-generation polymer overcoats the seed polymer in a core-shell fashion. The encapsulation phenomena were observed and explained in terms of the microscopic thermo-dynamic environment of the latex particles.