Colloidal dispersions of polymer-silica nanocomposite particles were synthesized in high yield by homopolymerizing 4-vinylpyridine (4VP) in the presence of an ultrafine silica sol using a free-radical initiator in aqueous media at 60°C. Copolymerization of 4VP with methyl methacrylate and styrene also produced colloidally stable nanocomposite particles, in some cases for comonomer feeds containing as little as 6 mol % 4VP. However, homopolymerization of styrene or methyl methacrylate in the presence of the silica sol did not produce nanocomposite particles in control experiments. Thus a strong acid-base interaction between the silica sol and the (co)polymer appears to be essential for nanocomposite formation. Transmission electron microscopy studies confirmed the presence of the ultrafine silica sols within the nanocomposite particles, which typically exhibited "currant-bun" particle morphologies. This is in contrast to the "raspberry" particle morphologies previously reported for conducting polymer-silica nanocomposite particles. The average silica contents and mean particle diameters of the vinyl (co)polymer-silica nanocomposites were surprisingly insensitive to the synthesis conditions, as judged by thermogravimetric analysis and disk centrifuge photosedimentometry studies, respectively. The latter technique also indicated that some of the copolymer-silica dispersions were appreciably flocculated, although the degree of dispersion could be improved by redispersion in alkaline media. 1 H NMR spectroscopy studies on the extracted nanocomposites confirmed incorporation of the 4VP comonomer, with reasonable agreement between copolymer compositions and comonomer feeds being obtained. Aqueous electrophoresis measurements confirmed that the surface of the 4VP-silica particles is polymer-rich, which is consistent with their currant-bun morphology. Timeresolved photon correlation spectroscopy studies during nanocomposite formation showed that particle growth occurred rapidly, with particles reaching their final size after approximately 1 h. Doubling the 4VP monomer concentration at a fixed 4VP/silica ratio led to an increase in particle size from 150 to 220 nm. IntroductionIn polymer nanocomposites the polymer chains are confined to nanoscale (1-10 nm) dimensions. Following pioneering work by Giannelis and co-workers, 1,2 it is now recognized that these materials can exhibit unusual, even unique, properties 3 which cannot be obtained simply by comixing the polymeric component with the inorganic phase. 4,5 In many literature reports polymer nanocomposites are synthesized by creating or modifying the inorganic phase in the presence of preformed polymer chains. For example, Messersmith and Stupp 6 prepared calcium aluminate in the presence of various water-soluble polymers and obtained "organoceramic" materials. In contrast, Mark and co-workers 7 prepared monolithic poly(methyl acrylate)/SiO 2 nanocomposites by dispersing surface-modified silica particles in methyl acrylate, followed by polymerization of the monomeric con...

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Poly(N-vinylpyrrolidone)-stabilized polystyrene (PS) latexes have been coated with thin overlayers of polyaniline (PANi) to produce electrically conductive “core−shell” particles. In this work we focused on the morphology of the PANi overlayer, the colloid stability of the coated latexes, and electrical conductivity. PANi-coated particles exhibit a nonuniform morphology as observed by scanning electron microscopy (SEM), in comparison with the relatively smooth polypyrrole overlayers synthesized in a previous study (Lascelles, S. F. et al., J. Mater. Chem. 1997, 7, 1339 and 1349). Disk centrifuge photosedimentometry confirmed that the PANi-coated PS latexes were weakly flocculated. The underlying PS latex “core” was quantitatively removed by solvent extraction, and SEM observations of the PANi residues revealed a “broken egg shell” morphology. Vibrational bands due to the PANi component were more intense in both the FT-IR and Raman spectra of the PANi-coated PS latexes, which is also consistent with the “core−shell” morphology. No reduction in the surface roughness of the PANi overlayer was observed when the rate of the aniline polymerization was decreased or if the latex surface was pretreated with either a thin polypyrrole overlayer or a layer of adsorbed surfactant. Similarly, only rough PANi overlayers were observed when coating a sulfonated PS latex. However, a more uniform deposition of PANi and a corresponding improvement of colloid stability were obtained using aniline hydrochloride monomer in the absence of added acid.

A new methodology for the preparation of addressed DNA matrices is described. The process includes an electrochemically directed copolymerization of pyrrole and oligonucleotides bearing on their 5' end a pyrrole moiety introduced by phosphoramidite chemistry. The electro-controlled synthesis of the copolymer (poly-pyrrole) gives, in one step, a solid conducting film deposited on the surface of an electrode. The resulting polymer consists of pyrrole chains bearing covalently linked oligonucleotide. The polymer growth is limited to the electrode surface, so that it is possible to prepare a DNA matrix on a multiple electrode device by successive copolymerizations. A support bearing four oligonucleotides was used to detect three ras mutations on a synthetic DNA fragment.

The surface compositions of seven polyaniline (PAni)-coated polystyrene (PS) latexes have been investigated by X-ray photoelectron spectroscopy. This technique was used to assess the uniformity of the PAni overlayers deposited onto micrometer-sized, poly(N-vinylpyrrolidone) (PNVP)-stabilized PS latex particles under various synthesis conditions. Peak fitting of the N(1s) core-line spectra provided evidence for the presence of both PAni and the PNVP stabilizer at the surface of the PS latex. Nonuniform PAni coatings were obtained using conventional aniline polymerization conditions (aniline monomer, ammonium persulfate, 1.2 M HCl at 25 °C). In contrast, more homogeneous PAni coatings were obtained when polymerizing aniline hydrochloride at 0 °C in water. The relative proportion of PAni at the surface of the PS latex was estimated by comparing the surface nitrogen contents of the coated and uncoated PS latexes to that of a PAni “bulk powder” prepared in the absence of any latex. It was shown that the relatively rapid polymerization at room temperature resulted in nonuniform PAni coatings and reduced PAni surface composition. The maximum PAni coverage was found to be around 57−59%, which is much lower than the surface composition of 94−100% found for polypyrrole (PPy) deposited onto a similar micrometer-sized PS latex (Perruchot et al. Langmuir 1996, 12, 3245). These results indicate that the PAni coatings are much less uniform than the PPy overlayers. Finally, the improved uniformity of the PAni overlayers prepared using aniline hydrochoride in the absence of HCl is consistent with the higher coalescence temperature found for these PAni-coated PS particles in hot-stage optical microscopy studies.