A simple method for producing micron-sized, highly monodisperse polystyrene particles in aqueous media: Effects of impeller speed on particle size distribution

摘要

The single stage polymerization recently proposed for producing micrometer-sized polymer particles in aqueous media was carried out with styrnee monomer, potassium persulfate initiator and dimethyldodecylbetaine amphoteric surfactnat in ranges of impeller speed (250-500 rpm) and addition time of the surfactnat to the system (5-30 min) at a monomer concentration of 1.1 mol/dm~3H_2O and initiator concentrations of 4 and 8 mmol/dm~3H_2O. Particle size distribution and monomer-to-polymer conversion were measured during the polymerizations. It was shownthat the addition of small amount of the surfactnat (0.5 mmol/dm~3H_2O) was effective to promote the coagulation of particles, which led to the production of monodisperse, micrometer-sized polymer particles. The particle size distribution significantly depended on impeller speed. At the lowest impeller speed of 250 rpm, secondary particles were generated during the reaction and the size distribution of final particles was bimodal. The generation of secondary particles is explained from an increase in electric surface potential of polymer particles during the reaction. At impeller speeds above 250 rpm, particle size distributions were unimodal throughout the reaction and the average diameter of final particles increased with a decrease in impeller speed. Particles produced at 300 rpm had an average diameter of 2 #mu#m and the highest monodispersity with a coefficient of variation of size distribution of 3.4% that is much smaller than typical monodispersity criterion of 10%.