In
a previous article, it was reported that a rather amount of
sulfate end-groups as initiator fragment were buried in the inside
of polystyrene (PS) particles, which were synthesized by emulsion
polymerization with potassium persulfate initiator and nonionic emulsifier
and operated to absorb water from the aqueous medium, resulting in
hollow particles, when the PS emulsion was treated at higher temperature
than the glass transition temperature of PS. In this article, it was
clarified that the water absorption is based on the osmotic pressure
between the outside (aqueous medium) and inside of the PS particles
due to the buried sulfate end-groups.