Micron-size crosslinked polystyrene (MCPS) microspheres were prepared by the dispersion copolymerization of styrene/2,2'-oxy-bisethanol diacrylate in the solvent mixture of ethanol/n-heptane. 2,2'-Azobisisobutyronitrile (AIBN) and poly (N-vinyl pyrrolidone) (PVP) were used as initiator and steric stabilizer, respectively. Changing the ratio of ethanol/n-heptane can change the polarity of the dispersion medium. The effects of concentrations of monomer, initiator, stabilizer and crosslinking agent and the polarity of medium on polymerization kinetic, particle size, and size distribution were investigated through three polymerization methods: Batch, all addition and post-addition seeded dispersion polymerization. MCPS microspheres were obtained in the size of 7.0 mum with narrow size distribution and 5.0% crosslinker level under post-addition seeded polymerization. (C) 2002 Elsevier Science B.V. All rights reserved.