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

No abstract

A new "grafting from" strategy based on surface-initiated atom transfer radical polymerization (ATRP) was first used for the preparation of a polymer-based ion-exchange support for HPLC. The most important property of the proposed method is to be applicable for the synthesis of any type of ion exchanger in both the strong and the weak forms. Monodisperse, porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.8 mum in size were synthesized by "modified seeded polymerization". Poly(dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The ATRP initiator, 3-(2-bromoisobutyramido)propyl(triethoxy)silane was covalently attached onto poly(DHPM-co-EDM) particles via the reaction between triethoxysilane and diol groups. In the next stage, the selected monomer carrying strong cation exchanger groups, 3-sulfopropyl methacrylate (SPM), was polymerized on the initiator-immobilized particles via surface-initiated ATRP. The degree of polymerization of SPM (i.e., length of polyionic ligand) on the particles was precisely controlled by adjusting ATRP conditions. Poly(SPM)-grafted poly(DHPM-co-EDM) particles obtained with different ATRP formulations were tried as chromatographic packing in the separation of proteins by ion-exchange chromatography. The proteins were successfully separated with higher column yields with respect to the previously proposed materials. The plate heights between 100 and 150 mum were achieved with the column packed with the particles carrying the shortest poly(SPM) chains. The plate height showed no significant increase with increasing flow rate in the range of 0.5-16 cm/min.

ABSTRACT:In this study, the monodisperse-macroporous particles produced by a relatively new polymerization protocol, the so-called, "modified seeded polymerization," were used as column-packing material in the reversed phase chromatography (RPC) of proteins. The particles were synthesized in the form of styrene-divinylbenzene copolymer approximately 7.5 m in size. In the first stage of the synthesis, the monodisperse polystyrene particles 4.4 m in size were obtained by dispersion polymerization and used as the "seed latex." The seed particles were swollen by a low-molecular-weight organic agent and then by a monomer mixture. The monodisperse-macroporous particles were obtained by the polymerization of monomer mixture in the seed particles. In the proposed polymerization protocol, the number of successive swelling stages was reduced with respect to the present techniques by the use of sufficiently large particles with an appropriate average molecular weight as the seed latex. A series of particles with different porosity properties was obtained by varying the monomer/ seed latex ratio. The separation behavior of HPLC columns including the produced particles as packing material was investigated in the RPC mode using a protein mixture including albumin, lysozyme, cytochrome c, and ribonuclease A. The chromatograms were obtained with different flow rates under an acetonitrile-water gradient. The theoretical plate number increased and chromatograms with higher resolutions were obtained with the particles produced by using a lower monomer/seed latex ratio. The separation ability of the column could be protected over a wide range of flow rates (i.e., 0.5-3 mL/min) with most of the materials tested.