Water-soluble polyurethane resins as emulsifiers in emulsion polymerization of styrene: Nucleation and particle growth

Polystyrene/polyurethane hybrid latex particles were synthesized by employi ng water-soluble (or dispersible) polyurethane resins which had been prepar ed from isophorone diisocyanate (IPDI), poly(1,2-propylene glycols) (PPG-75 0 and PPG-2000), and 2,2-bis(hydroxy-methyl)propionic acid (DMPA). Two kind s of polyurethane resin were used as emulsifiers and their effect on emulsi on kinetics was investigated by measuring the rate of polymerization, the p article size distribution, the number of particles, and the average number of radicals per particle. Effects of the resin concentration on the rate of polymerization and the number of particles were found to have a somewhat s imilar kinetic behavior with exponents in the range of 0.25-0.30 and 0.60-0 .70, respectively. The average particle sizes, however, were very small (ca . 40-60 nm) and the particle size distribution showed a broad distribution. The particle nucleation period continued over 0.7-0.8 fractional conversio n of styrene. Moreover, the initial latex particle size was very large in c omparison with the final particle size. Characteristic behavior of the part icle nucleation and growth was mainly attributed to superior solubilizing a bility and high internal viscosity of the polyurethane resin aggregates.