SYNOPSISMonosize polystyrene microbeads were prepared by dispersion polymerization in different alcohol/ water media. Azobisisobutyronitrile and polyacrylic acid were utilized as initiator and steric stabilizer, respectively. The polymerizations were performed in three kinds of dispersion media having different polarities: isopropanol/water, 1-butanol/water, and 2-butanol/water. The effects of initiator and stabilizer concentrations, alcohol/water ratio, and monomer /dispersion medium ratio on the size and monodispersity of the polymeric microbeads were investigated. By dispersion polymerization, polystyrene ( PS ) microbeads were obtained in the size range of 1.0-4.0 pm with narrow size distribution or in the monosize form. The average size and size distribution of microbeads decreased with increasing polarity of the dispersion medium. The average size and size distribution increased with increasing initiator concentration in all dispersion media. The increase in the stabilizer concentration in homogeneous dispersion media resulted in a decrease in average size and size distribution of the microbeads. A clear increase was observed in the average size with increasing monomer /dispersion medium ratio. Isopropanol/water dispersion medium provided monosize microbeads with higher values of monomer/dispersion medium ratio. I NTRO DU CTlO NMany applications in the biomedical field, information industry, and microelectronics require the use of polymeric particles of controlled size and surface properties. Traditionally, micron-size particles have been prepared by suspension polymerization, where monomer droplets are broken into the micronsize range within a dispersion medium by homogenization in the presence of a stabilizer, and subsequently are polymerized by using a monomer phase soluble initiator. This technique is usually used for the production of spherical polymeric particles between about 50-1000 pm. A wide particle size distribution is usually observed because of inherent size distribution in the mechanical homogenization step and because of the coalescence problem faced in this type of polymerization.

SYNOPSISIn this study, monosize polystyrene (PS) latices were prepared by dispersion polymerization of styrene in isopropanol-water media using poly (acrylic acid) (PAA) as a steric stabilizer and 2,2'-azobisizobutyronitrile ( AIBN) as an initiator. The effects of initiator and stabilizer concentrations, alcohol/water and monomer/dispersion medium ratio on the polymerization kinetics, and the size and monodispersity of PS latices were experimented with in a stirred reactor system. Monosize PS beads in the size range of 1.0-3.0 pm were obtained. The PS latex obtained in the first step having a diameter of 2.3 pm were used as the seed latex, and styrene/acrylate monomers, acrylic acid ( AA), 2-hydroxyethyl methacrylate (HEMA), and dimethylaminoethyl methacrylate ( DMAEMA) were copolymerized onto the PS latex particles. The incorporation of functional groups to the surface and bulk structure of PS was confirmed by IR, FTIR, XPS, and zeta potential measurements. 0 1994

This article demonstrates that geometric analysis by itself is not enough to evaluate Alexander’s wholeness in public spaces and that his theories of wholeness can—and should—be extended into the realm of events. The first section provides a summary of the theory of centers and the relevance of events with regard to the theory of wholeness. In the second section, a new way to classify centers is presented, along with insights from Alexander’s works into an approach for incorporating event centers into the theory of wholeness. The final part puts these ideas to the test on a public square in Stuttgart, Germany, using a geometric analysis and an analysis of user activity to determine the performance of the square as a center. The research concludes that utilizing Alexander’s theories from an event-first rather than a geometry-first perspective is an approach especially well-suited for public spaces.