Synthesis of polystyrene particles with controlled size via emulsion and dispersion radical polymerization: A practical guide

Simple procedures to obtain monodisperse (Cv <= 5%) polystyrene nano- and microparticles with controlled diameters in the range of 164 nm-4.1 mu m via emulsion, soap-free emulsion and dispersion polymerization methods were developed. It was demonstrated that the reactor form and stirring speed are crucial factors influenced the particle size and particle size distribution as well as reproducibility of experiments. Furthermore, it was found that in emulsion radical polymerization of styrene with sodium dodecyl sulfate as surfactant the particle size could be easily controlled by varying the concentration of surfactant and monomer. In this way, particles with diameters ranging from 110 to 670 nm and a coefficient of variation of less than 5% were obtained. Production of larger particles was accomplished via dispersion polymerization of styrene in different solvents. The most suitable solvent for obtaining particles with a diameter in the range of 0.7-1.7 mu m was found to be ethanol and its mixtures with water, where the particle size control can be accomplished by varying the ethanol/water ratio or the concentration of stabilizer. It was shown that substitution of ethanol by less polar isopropyl alcohol allowed to prepare larger monodisperse spherical polystyrene particles. The particle size can be tuned in the range between 0.9-4.1 mu m (Cv <= 5%) by the change of the monomer concentration. The novelty of this study consists in the development of a reproducible methodology for the preparation of monodisperse polystyrene particles with the predictable size in the size range between 160 nm to 4.1 mu m, which represents significant interest for encapsulation of quantum dots and magnetic nanoparticles for the application in catalysis, diagnostic and biotechnology.