Styrene (hydrophobic monomer), methyl methacrylate (MMA, hydrophilic monomer, almost 100 times more soluble in water than styrene) and nonionic emulsifier are often used in general emulsion polymerizations in industrial production. To clarify the effect of stirring for 100 min at 70 1C before starting emulsion polymerization with a nonionic emulsifier (polyoxyethylene nonyl phenyl ether, E911) and potassium persulfate as the initiator for the particle formation, the emulsion homopolymerization of styrene and MMA was carried out at different stirring rates (0-500 r.p.m.) at 70 1C. Immediately before the start of the polymerization, in the case of styrene, partitioning of components in the system nearly reached an equilibrium state at 500 r.p.m., whereas the system was in a nonequilibrium state at 240 r.p.m. In the case of MMA, the system nearly reached an equilibrium state even at 240 r.p.m. Polystyrene particles were obtained as B100-nm-sized spherical particles at 240 r.p.m. and as B1-lm-sized 'bur-like' nonspherical particles at 500 r.p.m., whereas poly(MMA) particles were B100-nm-sized and almost spherical at both stirring rates. Monomer polarity strongly affected the partitioning of the monomer to the aqueous phase and the nonionic emulsifier to the monomer phase before starting the emulsion polymerization, resulting in the differences in particle formation and the incorporation of nonionic emulsifier inside the polymer particles.

Emulsion polymerization of styrene with a nonionic emulsifier (polyoxyethylene nonylphenyl ether, E911) and potassium persulfate as initiator was carried out at different stirring rates (240-500 rpm) at 70°C, which was started by the addition of initiator after stirring for 100 min at 70°C. Resulting polystyrene (PS) particles at 240 rpm were 70-nm-sized, spherical particles and incorporated only 5 wt.% of total E911. On the other hand, particles at 500 rpm were 1-μm-sized, nonspherical particles, which were formed by coagulation of small particles, and incorporated above 70 wt.% of E911 in the inside. Before starting emulsion polymerization, E911 and styrene, respectively, transferred from an aqueous phase to a styrene phase and from the styrene phase to the aqueous phase (water and micelles) faster at 500 rpm than 240 rpm. At 240 rpm, there were a lot of almost empty micelles (ca. 5 nm) in the aqueous phase, on the other hand at 500 rpm, 70 wt.% of total E911 transferred to the styrene phase and the micelles were swollen with much monomer (ca. 40 nm) even if the number was smaller. Stirring prior to starting the emulsion polymerization greatly affected partitionings of monomer to the aqueous phase and the nonionic emulsifier to the styrene phase, resulting in the differences in the particle formation and the incorporation of the nonionic emulsifier inside PS particles.