Magnetic polystyrene latex

Preparation of Magnetic Polystyrene Latex Covered by PNIPA Gel Shell. . 149... 

The magnetic polystyrene latex particles with diameter of 120 nm were covered by PNIPA gel layer. The mPS latex prepared according to the procedure described previously was strongly stirred at 60 °C and kept under N2 atmosphere for 1 h. Then, 0.05 g APS and 0.5 mL 1 M NIPA solution were added to the mPS latex and the reaction mixture was stirred at 60 °C for more than 1 h. Then, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added. After 2 h, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added again to the mixture. This mixture was stirred 60 °C for more than 2 h under N2 atmosphere. Figure 9 shows the structure of the core-shell microsphere in dry state. 

Csetneki 1, Faix MK, Szilagyi A, et al. (2004) Preparation of magnetic polystyrene latex via the miniemulsion polmerization technique. J Polym Sci Part A Polym Chem 42 4802-4808... 

Using miniemulsion polymerization, Gu et al. reported the synthesis of magnetic polystyrene latex and carboxylated magnetic polymer latex [173, 174]. In the lat-ter,carboxyl end groups were provided on the surface of the latex directly from the initiator 4,4-azobis (4-cyanopentanoic acid) (ACPA). The average size of the final magnetic particle was 250 nm. 

Mori and Kawaguchi reported the preparation of magnetic polystyrene particles containing 30 wt% of magnetite. Magnetic polystyrene particles of 300 nm were produced and easily separated when persulphate, KPS or APS initiator was used. Conversely, due to high colloidal stability, the latex prepared by oil-soluble initiator (for instance AIBN) was not easy to separate, and the magnetite nanoparticles were located on the surface of the polystyrene latex. A mixture of initiators resulted in intermediate properties compared to individual systems [170]. 

The representative NP probes include semiconductor NPs (quantum dots), gold NPs, polystyrene latex NPs, magnetic NPs and dye-doped NPs. In our laboratory, dye-doped silica NPs have been developed. 

Recently, membranes with SP nanoparticles have been introduced which operate on a slightly different principle, as illustrated in Fig. 13.7. The membranes contain an ordered array of stimuli-responsive core-shell type magnetic polystyrene latex particles. The particles change their size in response to external stimuli, acting as on-off switches or permeability valves , regulating the permeation through membrane channels. 

Numerous studies on bead bio chips were therefore based on magnetic [16,17], glass or silica [18-20], and polystyrene beads [21]. The DNA immobilization chemistry of those beads could be very different, from the classical avidin/biotin affinity reaction [17,22] (Fig. 2B) to the disulfide bridging onto thiol modified silica [19] (Fig. 5A), the thiocyanate reaction onto amino-terminated latex beads [21] (Fig. 5B), and finally the hybridization-based immobilization of poly(A)-tagged probes onto poly(T)-bearing magnetic beads [16] (Fig. 5C). 

Emulsion polymerization techniques have also been used for the direct encapsulation of magnetic particles [113,114]. A double layer of surfactant was generally used (sodium oleate combined with sodium dodecyl benzene sulfonate). The method yielded up to 20 wt% of encapsulated magnetite into polystyrene polydis-perse latex particles. Sometimes, the formation of large amounts of coagulum could not be avoided [113a]. 

J. Lee, M. Senna, Preparation of monodispersed polystyrene microspheres uniformly coated by magnetite via heterogeneous polymerization. Colloid Polym. Sci. 1995,273, 76-82 (c) F. Camso, A.S. Susha, M. Giersig, H. Moh-wald. Magnetic core-shell particles preparation of magnetite multilayers on polymer latex microspheres, Adv. Mater. 1999, 11,950-953. 

Polymer latex nanoparticles can be prepared in many materials such as polystyrene and acrylate with controllable size, through radical-initiated polymerization in heterogeneous media (Figure 14.2). The sizes of latex nanoparticles are very dependent on the polymerization conditions. To yield nanosized particles, the polymerization is usually carried out in miaoemulsions [34], For some applications, two or more monomers are used. For example, for polystyrene nanoparticles, divinylbenzene (DVB) is used as a cross-linker to improve the structural performance [35] and methacrylic acid (MAA) or methacrylate (MMA) is used as a co-monomer to provide the nanoparticles with desirable surface chemistry [36,37], Furthermore, some fluorochromes or magnetic materials are incorporated into polymer nanoparticles, to render the particles multifunctional [38,39],... 

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