Study of the effect of porogen amount on formation of uniform polystyrene hollow particles prepared by SPG membrane emulsification technique

Uniform polystyrene (PSt) hollow particles were prepared by combining a Shirasu porous glass (SPG) emulsification technique and a subsequent suspension polymerization process. The oil phase mainly containing St, hydrophilic monomer, hexadecane (HD), and initiator, was pressed through the uniform pores of a SPG membrane into the continuous phase to form uniform droplets. Then, the droplets were polymerized at 70 degreesC. HD was used as a porogen for formation of hollow particles. The amount of HD was varied in order to clarify the formation mechanism. It was found that rapid phase separation between HD and PSt in the initial stage of polymerization was responsible for the formation of hollow particle. When HD amount was low, rapid phase separation was induced by the rapid diffusion of monomer into the aqueous phase. This is because a large amount of new particles occurred, which sucked up greedily monomer from the aqueous phase. On the other hand, when HD amount was high, rapid phase separation was promoted by a large amount of HD, even secondary nucleation was prevented by increasing HD