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Uniform polystyrene (PSt) particles with the size of 1.9 μm were first prepared via dispersion polymerization, and then used as the seeds in a second-stage dispersion copolymerization of styrene (St) and methacrylic acid (MAA) to produce carboxyl-carrying microspheres. The PSt seed particles were swollen by monomer mixture of St and MAA, including an oil-soluble initiator 2,2′-azobisiso-butyronitrile (AIBN), before polymerization. Finally, uniform PS/P(St/MAA) (polydispersity index, PDI = 1.02) microspheres with the size of 2.2 μm were obtained. The average particle size and size distribution of the final microspheres were investigated. MAA contents between 54 and 97 mg/g were detected from the PS/P(St/MAA) particles produced under different conditions. Dispersion medium has great influence on the kinetics of polymerization, due to its effect on the partitioning of monomers, solvents, and initiator in the particle phase, probably as well as on the conformation of the dispersion agent on the surface of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3586–3591, 2006

Micron-size functional crosslinked poly(methyl methacrylate) (PMMA) particles with narrow size distribution in the range of 1∼5 µm were prepared by dispersion copolymerization in polar media with poly(N-vinylpyrrolidone)(PVP) as steric stabilizer, 2,2′-azobisisobutyronitrile(AIBN) as initiator and ethylene glycol dimethylacrylate (EGDMA) as crosslinking agent. The effects of functional comonomer acrylic acid (AA) concentration, contents in AIBN, EGDMA and PVP, media polarity as well as reaction temperature on the particle size and size distribution were investigated. Particle size initially increased, and then decreased with increasing AA concentration in the range of 0.7∼3.5 mol l−1, having a maximum of 5.01 µm at the concentration of 2.1 mol l−1, while size distribution became broader. This was regarded as the result of different roles of PAA in the process. Particle size increased with decreasing media polarity and stabilizer concentration, and with increasing initiator concentration and reaction temperature. The resulting particle shapes were observed by transmission electron microscopy and the presence of carboxyl groups on the surface of the particles was confirmed by Fourier-transform infrared spectroscopy. Copyright © 2003 Society of Chemical Industry

Monodisperse highly crosslinked microspheres were prepared by dispersion copolymerization of styrene and divinylbenzene in an ethanol/water medium using poly(N-vinylpyrrolidone) (PVP) as the stabilizer. The locus of polymerization and growth of particles were investigated. The polymerization kinetics, average particle diameter (D n ), polydispersity index (PDI), and numbers of particles (N p ) were presented. When the initial styrene concentration is below 20%, the results indicate that the polymerization occurs in the particles, and the particles grow to their final size by the diffusion of monomer and oligomer into the existing particles. The polymerization rate can be described by the equation R P = k[l] 0.87 ([St] 1.91 + [DVB] 0.09 )(1 + [PUP] 0.01 exp(- 45.35/RT). The data from infrared spectroscopy demonstrated that the graft stabilizer was present. The dissolution experiments show that the crosslinking reaction occurred irregularly in batch dispersion polymerization. Using the postaddition approach, up to 3% divenylbenzene (DVB) was successfully incorporated in the synthesis of coagulum-free substance, and monodisperse crosslinked 5 μm microspheres with a superior resistance to solvents have been prepared.