Abstract: Uniform polymer microspheres were prepared through precipitation polymerization of pentaerythritol triacrylate (PETA) and styrene in ethanol or an ethanol-water mixture using azobisisobutyronitrile (AIBN) as initiator. The effects of the polymerization time, amount of PETA, and water content in the mixed solvent on the polymerization process and the microspheres were studied. Uniform microspheres were readily obtained when the amount of PETA was between 5% and 35% (mass fraction) relative to all monomers with a polymerization time of 6 h. When the mass fraction of PETA was <20%, the microspheres decreased in size and became more uniform as the PETA mass fraction increased. By contrast, when the PETA mass fraction was >20%, the microspheres size increased and the size distribution became larger as the PETA mass fraction increased. With the ethanol-water binary solvent mixture, the monomer conversion and microsphere yield increased compared with those obtained with pure ethanol. However, the water volume fraction needed to be kept below 30%, above which the uniformity of the microspheres was deteriorated. Based on the results, the mechanism of microsphere formation is discussed.

Key words: Uniform polymer microsphere, Precipitation polymerization, Ethanol-water mixed solvent, Pentaerythritol triacrylate, Styrene