Fully crosslinked, stable poly(styrene‐co‐divinylbenzene) microspheres, which are composed of various concentrations of divilylbenzene from 5 to 75 mol % based on styrene monomer, were prepared without a significant particle coagulation by the precipitation polymerization. The number‐average particle diameter ranged from 3.5 to 2.8 μm and decreased with an increasing concentration of divinylbenzene in monomer. In addition, the coefficient of variation of the microspheres was slightly reduced with the increasing concentration of divinylbenzene. The circularity and the measured specific surface area indicated that lesser particles are coagulated because of the improved stability of individual particles at a high divinylbenzene concentration and that the resulting particles have a smooth surface without micropores. The glass‐transition temperature was not observed for all microspheres formed from the range of divinylbenzene concentrations. In addition, the onset of the thermal‐degradation temperature was increased from 339.8 to 376.9 °C upon higher contents of divinylbenzene. On the basis of the DSC and thermogravimetric data, the polymer microspheres prepared by the precipitation polymerization possessed a fully crosslinked structure and highly enhanced thermal stability. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 835–845, 2004

In this work, we produced large-area graphene oxide (GO) sheets with fewer defects on the basal plane by application of shear stress in solution to obtain high-quality reduced graphene oxide (RGO) sheets without the need for post-annealing processes. This is described as rheologically derived RGO. The large-area GO sheets were generated using a homogenizer in aqueous solution, which induced slippage of the GO in the in-plane direction during the exfoliation process, in contrast with the conventional sonication method. The effects of chemical reduction under mild conditions demonstrated that the formation of structural defects during the exfoliation process affected the RGO properties. In the Raman spectra, the I(D)/I(G) ratio of the homogenized RGO (HRGO) increased more than that of the sonicated RGO (SRGO) due to the large number of ordered six-fold rings on the basal plane. The enhanced sheet resistance of the HRGO thin film was found to be 2.2 kΩ/sq at 80% transmittance. The effective exfoliation method has great potential for application to high-performance RGO-transparent conducting films.

The synthesis and application of polymeric microspheres are of great importance from both academic and industrial points of view. As polymeric microspheres have been used in wider fields of conventional 1 and more sophisticated 2-6 areas, the development of a new process to prepare such materials has received much attention. Polymer microspheres of a particular size and uniformity are generally obtained with one of the heterogeneous polymerizations, including suspension, emulsion, dispersion, seeded, and precipitation polymerizations. Moreover, each polymerization is branched to several subsidiary methods, such as macroemulsion, miniemulsion, microemulsion, and soap-free emulsion polymerizations.Fully crosslinked monodisperse polymer microspheres have unique applications because of their superior strength, thermal and solvent resistance, and antislip properties.7 However, the synthesis of such microspheres is limited to a few techniques, such as seeded polymerization, [8][9][10][11] Shirasu porous glass (SPG) membrane emulsification followed by postpolymerization, 12,13 and precipitation polymerization.14 Precipitation polymerization, in particular, has advantages over the other techniques because crosslinked microspheres can be readily prepared in a single process without any auxiliary apparatus to make the size distribution of the particles narrow. Therefore, homoand copolymerization systems have been thoroughly investigated, including poly(divinylbenzene), 15 poly (methacrylic acid-co-polyethylene oxide methyl ether methacrylate), 16 poly(methacrylate-co-divinylbenzene), 17 poly(chloromethylstyrene-co-divinylbenzene), 18 poly(divinylbenzene-co-maleic anhydride) 19 , poly(methyl methacrylate-co-divinylbenzene)[poly(MMA-co-DVB)], [20][21][22] and poly(styrene-co-divinylbenzene) [poly(St-co-DVB)]. 23In addition, mechanistic studies to elucidate the formation of stable microspheres in the absence of any stabilizer have been reported 24,25 in which the absorption of oligomeric species onto the nuclei and the high degree of crosslinking are the primary reasons for the formation and stable growth of the microspheres.Several examples of the copolymerization of the partially water-soluble monomer acrylamide (AAm) and oil-soluble monomers such as methacrylic acid 26 and styrene 27,28 have been recently reported with precipitation polymerization, 26 inverse microemulsion polymerization, 27 and water/oil/water emulsion by SPG membrane emulsification and subsequent suspension polymerization. 28In our previous studies, poly(St-co-DVB) and poly (MMA-co-DVB) microspheres containing various concentrations of divinylbenzene (DVB), from 5 to 75 mol %, were synthesized by precipitation polymerization, and their unexpected thermal properties, superior to those of crosslinked polymers prepared by emulsion and

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Polymer particles are important materials because of their versatile applications, including coatings, adhesives, inks, leather finishing, construction, and so on. 1 Recently, such polymer colloids have been used in advanced fields such as information technology, electric and electronic science, and biotechnology. 2,3 Because of the transition of these applications, precise control of properties of these polymer particles has become more important. Fully crosslinked polymer microspheres have also been receiving considerable attention because of their improved thermal, chemical, and physical properties. However, synthesis of such polymer colloids is technically difficult.Precipitation polymerization, which was developed by Stöver's group, 4 provides a simple pathway to synthesize fully crosslinked spherical polymer particles. The uniqueness of the precipitation polymerization lies in the absence of any stabilizing agent such as surfactants or steric stabilizers for obtaining spherical particles. In precipitation polymerization, the formation of stable spheres is achieved by means of a self-stabilizing mechanism via crosslinking of polymer chains. Because a high level of crosslinking is developed in individual particles, coagulation between the particles is prevented because of the hard and resilient nature of each particle. The advantage of precipitation polymerization would be the facile preparation of highly crosslinked micrometer-sized particles with monodisperse or narrow size distribution. These materials are used in highend products such as packing materials in column chromatography or spacers in liquid crystal displays because of their superior strength, thermal and chemical resistance, and antislip properties. 5 Various monomers including methacrylate, 6 maleic anhydride, 7 and chloromethyl styrene 8 have been copolymerized to form miscrospheres with divinylbenzene (DVB) as the crosslinkable monomer with precipitation polymerization. Our group has also conducted precipitation polymerization of various compositions of styrene (S) and DVB and found unexpected superior thermal properties because of the fully crosslinked microstructure of the microspheres. 9 Furthermore, we have reported the mechanism 10 of precipitation polymerization based on the surface properties of the microspheres, and the comparison 11 with dispersion polymerization based on the variation of the final size with respect to the polymerization ingredients.According to these previous studies, a low monomer concentration should be used for forming individually stable microspheres without coagulation in precipitation polymerization. Low monomer concentration is the disadvantage in the process. In this study, poly(methylmethacrylate-co-divinylbenzene) [poly(MMA-co-DVB)] microspheres are prepared by precipitation polymerization under various concentrations of polymerization ingredients to increase the monomer concentration in the polymerization system.Polymerization was carried out in a shaking water bath with an agitation speed in the range o...