PARTICLE FORMATION AND CATALYZED AGGLOMERATION IN EMULSION POLYMERIZATION

Catalyzed agglomeration, restricted to the particle formation phase of emulsion polymerization, can be used to distinguish experimentally whether or not a homogeneous nucleation mechanism is operative in a given persulfate-initiated emulsion polymerization system. The agglomeration catalyst used had a mode of action disclosed in earlier work, which proves that a homogeneous and not the generally accepted micellar nucleation mechanism is effective in a persulfate-initiated polymerization system even for monomers of low water solubility, such as styrene and butadiene, and emulsifier concentrations > cmc. Using catalyzed agglomeration, particle size and the monodispersity coefficient as well as the particle formation time were investigated as a function of monovalent cation concentration, emulsifier concentration and polymerization temperature. All correlations found either were consistent with homogeneous nucleation or completely excluded micellar nucleation. This means that poor water solubility of monomers like styrene and butadiene can no longer be a criterion for micellar nucleation. Homogeneous primary particle formation followed by agglomeration, which may be more or less pronounced or—in a few cases—does not occur at all, is most applicable and seems to be the particle formation mechanism generally valid for persulfate-initiated emulsion polymerization. © 1990, American Chemical Society. All rights reserved.