Micron-size crosslinked microspheres bearing carboxyl groups via dispersion copolymerization

Micron-size crosslinked polystyrene microspheres in the range of 2-33 μm, bearing carboxyl groups were prepared via dispersion copolymerization of styrene (St), acrylic acid (AA) and ethylene glycol dimethacrylate (EGDMA) in water/ethanol media, using poly(N-vinylpyrrolidone) (PVP) as stabilizer and 2,2′-azo-bisisobutyronitrile (AIBN) as initiator. The effects of concentration of functional monomer (AA) and crosslinking monomer (EGDMA), as well as water/ethanol ratio on particle size and distribution were investigated. It has been found that, increasing the concentration of AA and EGDMA would increase particle size and distribution. However, particle size decreased but particle size distribution increased, as the ratio of water/ethanol increased. The distribution of carboxyl groups was greatly affected by the concentration of reactants and the water/ethanol ratio in the media. The particles formed will be more hydrophylic in the core, but more hrdrophobic in the shell, with increasing AA or St concentration. This result is reversed when crosslinking monomer (EGDMA) concentration or water/ethanol ratio was increased.