High solids vinyl acetate polymers from miniemulsion polymerization

High solids content (50%) poly(vinyl acetate) latexes have been prepared from miniemulsion polymerization stabilized using SDS (sodium dodecyl sulfate) or a combination of SDS and nonionic surfactant nonylphenol ethoxylate (Triton X 405) and hexadecane as hydrophobe. The conditions for preparing stable monomer miniemulsion in terms of osmotic and Laplace pressures are discussed. Upon polymerization initiated by ammonium persulfate (APS), one observes in about all cases a decrease of the number of polymer particles as compared to the number of monomer droplets. These two numbers are much more close if the solid content is decreased to 20%, so that the discrepancy can be explained from collisions occurring between the polymer particles and the droplets not yet initiated. Conductometric titration of the serum allows to estimate the coverage of the droplets by the surfactants; further, it can be demonstrated that a part of the SDS is desorbed from the polymer particles that are partly stabilized by the charges coming from the initiator.