Preparation of Micron-sized Monodisperse Poly (Styrene-co-methyl Methacrylate) Microspheres by Dispersion Copolymerization

Abstract

Micron-sized monodisperse copolymer microspheres were prepared by dispersion copolymerization of styrene (St) and methyl methacrylate (MMA) in ethanol/water medium using 2,2'-azobis (isobutyronitrile) (AIBN) and poly (vinyl pyrrolidone) (PVP) as initiator and steric stabilizer, respectively.The effect of several important polymerization parameters such as polarity of the medium, concentrations of stabilizer, initiator, and monomers on the particle size and size distribution of the resulting particles were investigated.It was found that a higher MMA content in the reaction recipe requires a higher polarity of the medium in order to produce uniform poly (St-co-MMA) particles.A minimum value of the PVP concentration and a maximum value of the AIBN concentration should not be exceeded for the preparation of monodisperse copolymer microspheres.The particle size decreases with an increase of the PVP concentration when the PVP concentration is above the minimum value or an increase of the AIBN concentration when the AIBN concentration is below the maximum value.A lower monomer concentration is favorable to generate smaller microspheres, while larger microspheres can be obtained at a higher concentration of monomers.