Effect of electrolyte species on size of particle through soap-free emulsion polymerization of styrene using AIBN and electrolyte

The addition of electrolyte to a soap-free emulsion polymerization using oil-soluble initiator, 2,2^′-azobis(2-methylpropionitrile) (AIBN), was useful for production of the micron-sized polystyrene particle. To investigate the effect of electrolyte species on particle size, we focus on the counter ion and ionic radius of the cation during the synthesis of the particle. As a result, because the order of acid dissociation constant of the acid was HCl < HNO₃ < CH₃COOH, the suspension using chloride salt has lower pH and included the larger particles due to the coagulation growth process. Cation with a larger ionic radius could promote the particle growth strongly because its hydration was so weaker that it had the ability to reduce the thickness of the electrical double layer of negatively charged polystyrene particle. In summary, the addition of strongly acidic salt with larger cationic radius to the polymerization was efficient for making the size of polystyrene particle larger.