Practical aspects of the emulsifier-free emulsion polymerization of styrene

The influences of initiator concentration, ionic strength of the aqueous phase and styrene sulfonic acid sodium salt comonomer on the average particle size and particle uniformity of latexes generated via emulsifier-free emulsion polymerization of styrene has been studied. It was found that the average particle size increased with increasing initiator concentration in reactions where the ionic strength was not controlled. The uniformity of the latex particles decreased as the initiator concentration increased. It was also found that at a minimum initiator concentration of 1.5×10-3 M at a temperature of 80°, adequate conversion could not be obtained. This limited the range of particle sizes which could be produced without adding additional surfactants. It was also found that smaller particles, 0.135 μm diameter, could be formed by copolymerizing styrene sulfonic acid sodium salt with styrene. The effects of ionic strength on particle size was also investigated and it was found that the particle size increased with increasing ionic strength. At constant ionic strength, it was found that particle size decreased with increasing initiator concentration as expected theoretically.