Miniemulsion oxidative polymerization

Oxidative polymerization of aniline generates polyaniline nanoparticles using both inverse and direct miniemulsion polymerization techniques. ... 

Synthesis of polymer microspheres in the presence of magnetic nanoparticles, such as suspension polymerization or its modified versions, dispersion polymerization, surface-initiated radical polymerization, acid-catalyzed condensation polymerization, emulsion polymerization, mini-/microemulsion polymerization, in situ oxidative polymerization, inverse emulsion cross-linking, emulsion/double emulsion-solvent evaporation, and supercritical fluid extraction of o/w miniemulsion... 

As semiconducting polymers are normally difficult to process due to their low solubilities, several research groups have polymerized these polymers in miniemulsion, in order to improve their processibilities. The oxidative polymerizations (for details of monomers, see Figure 15.7) were carried out in miniemulsion, either in the droplets or on the surface of nanoparticles, in order to create an additional shell. 

Both, aniline and anilium hydrochloride were polymerized in direct and in inverse miniemulsion, respectively [140]. The polymerization of anilium hydrochloride, which was initiated by hydrogen peroxide, yielded a highly crystaUine emeraldine polyaniline. In direct miniemulsions, additional stabilizers (e.g., poly(vinyl pyrroU-done) or PVA) were employed to preserve colloidal stability. The polymerization of aniline in direct miniemulsion has also been reported [141] in this case, following polymerization the polymer was first treated with stannous chloride and then doped with p-toluenesulfonic acid. A dramatic increase in conductivity after treatment with stannous chloride was considered due to pernigraniline moiety in the emeraldine base structure having been reduced. Such oxidative polymerization of aniline may be used to add an additional conductive shell to preformed latexes. For example, Li et al. polymerized aniline in the presence of dodecylbenzesulfonic acid on the surface of polyurethane and polyurethane/poly(methyl methacrylate) nanoparticles prepared in miniemulsion [142]. 

The principle of miniemulsion polymerization to polyadditions of epoxyresins was successfully transferred to mixtures of different epoxides with varying diamines, dithiols, or diols which were heated to 60°C to form the respective polymers [125]. The requirement for the formulation of miniemulsions is that both components of the polyaddition reaction show a relatively low water solubility, at least one of them even below 10 5 g l1. The diepoxide bisphenol-A-diglycidylether was successfully used as epoxy component. In order to vary the obtained polymeric structure, tri- and tetra-functionalized epoxides were also used. As amino components a NH2 terminated poly(propylene oxide) with Mw=2032 g mol1, 4,4 -diaminobibenzyl, 1,12-diaminododecane, and 4,4 -di-aminodicyclohexylmethane were applied. As other addition components beside amine, 1,6-hexanedithiol and Bisphenol A were used. The hydrophobic compo-... 

Van Hamersveld et al. [176, 177] carried out hybrid miniemulsion polymerization of MMA, using HD as the costabihzer. In an attempt to encourage grafting, oxidized triglycerides (such as sunflower oil) were used as initiators. 

ATRP polymerization in miniemulsion has recently attracted more attention and met with greater success. Some difficulties with conventional initiation were attributed to catalyst oxidation during the homogenization/sonication step particularly when more active, less oxidatively stable, catalysts are used. This problem was solved using reverse ATRP or combinations of reverse and normal A I RP " that meant the catalyst could be added in its oxidized form (Section... 

Joumaa N, Toussay P, Lansalot M, et al. (2007) Surface modification of iron oxide nanoparticles by a phosphate-based macromonomer and further encapsulation into submicrometer polystyrene particles by miniemulsion polymerization. J Polym Sci Part A Polym Chem 46 327-340... 

Xu ZZ, Wang CC, Yang WL, et al. (2004) Encapsulation of nanosized magnetic iron oxide by polyacrylamide via inverse miniemulsion polymerization. J Magn Magn Mater 277 136-143... 

In contrast to the homogenous magnetite distribution by the three-step process, the dispersion of hydrophobized magnetite in styrene/MAA [ 173] or a toluene-based ferrofluid [174] in styrene, followed by a miniemulsion polymerization process, leads to magnetite/polymer particles with inhomogeneous iron oxide distribution. 

Taking into account all of the above mentioned applications, the synthesis of magnetic latex will be discussed in two parts first, the preparation of iron oxide nanoparticles and, second, the preparation of magnetic latex. Depending on the aim of researchers, many polymerization techniques are applied such as suspension, dispersion, emulsion, microemulsion and miniemulsion polymerization in combination with controlled radical polymerization techniques like atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) and nitroxide-mediated radical polymerization (NMP). The preparation of hybrid magnetic latex by emulsion polymerization will be the focus of this review. 

The effect of the amount of surfactant SDS, hydrophobe hexadecane, iron oxide magnetic particles, MAA and non-ionic cellulose ether, hydroxyethylcellulose, on the magnetic latex morphology, surface quality and size distribution was studied by Forcada et al. for the encapsulation of magnetic particles by miniemulsion polymerization of St. Optimal conditions were 2-3% of SDS, 9-12% of hexadecane, 10% of iron oxide and 2% of HEC, relative to the total amount of St and iron oxide [177]. 

Nanoparticles and nanocapsules resulting from the polymerization of styrene and/or divinylbenzene in miniemulsion, were produced in the presence of a polymerizable derivative of polyethylene oxide/polypropylene oxide, that was used to stabilize the droplets [54]. Subsequent X-ray photoelectron spectroscopy (XPS) measurements on dialyzed samples confirmed that the polymerizable surfactant... 

When conducting the ROMP of norbornene or cyclooctadiene in miniemulsions [82], two approaches were followed (i) addition of a catalyst solution to a miniemulsion of the monomer and (ii) addition of the monomer to a miniemulsion of Grubbs catalyst in water. With the first approach it was possible to synthesize stable latexes with a high conversion, whereas for the second approach particles of >400 nm were created, without coagulum, but with 100% conversion. Subsequently, a water-soluble ruthenium carbene complex [poly(ethylene oxide)-based catalyst] was prepared and used in the direct miniemulsion ROMP of norbornene [83], whereby particles of 200-250 nm were produced. The catalytic polymerization of norbornene in direct miniemulsion was also carried out in the presence of an oil-soluble catalyst generated in situ, or with a water-soluble catalyst [84] the reaction was faster when using the oil-soluble catalyst. Helical-substituted polyacetylene could be efficiently polymerized in direct miniemulsion to yield a latex with particles that ranged between 60 and 400 nm in size, and which displayed an intense circular dichroism [85] that increased as the particle size decreased. The films were prepared from dried miniemulsion latexes that had been mixed with poly(vinyl alcohol) (PVA) in order to conserve the optical activity. 

In a similar work, the synthesis of a composite with iron oxide particles and sul-fonated cross-linked polystyrene (SXLPS) for application in the PEMs for fuel cells was described (Brijmohan and Shaw 2007). The technique used for the polymerization was similar to the miniemulsion polymerization (Ramirez and Landfester 2003). However, some modification to the procedure was required to make the cross-linked and functional polymer-iron oxide composites. Also reported was the membrane fabrication process, which inclndes the alignment of synthesized particles in a high-performance snlfonated poly(etherketoneketone) (SPEKK) matrix (Gasa et al. 2006), and the properties of such PEMs for fuel cell applications. The final properties of the membrane depend on various factors, such as the lEC, the matrix, and the size of the particles. However, the main emphasis of the research was to demonstrate a useful membrane-fabrication technique that can be utilized to enhance the conductivity of the PEMs. 

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