Controlling morphology of polymer microspheres by Shirasu porous glass (SPG) membrane emulsification and subsequent polymerization: from solid to hollow

In this study, the solid, porous, and hollow polymer microspheres were prepared using a simple and novel production method based on Shirasu porous glass (SPG) membrane emulsification and suspension polymerization. With the SPG membrane, uniform-sized emulsion monomer droplets containing divinyl benzene (DVD), styrene (St), hexadecane (HD), and an initiator were prepared in an aqueous phase using a membrane emulsification technique. The aqueous phase contained hydroquinone (HQ) as a water-soluble inhibitor and polyvinylpyrrolidone (PVP) as a stabilizer. The morphology of the particles was affected by the stabilizer, St/DVB ratio, hexadecane amount, and initiator amount. Through this study, the porous polymer microspheres were achieved when the HD content was 30 wt% relative to the monomer and the hollow polymer microspheres was achieved when the HD content was more than 62.5 wt% relative to the monomer. These results highlight the phase separation speed between polystyrene (PSt) and HD.