The efficient, controlled polymerization of 2-hydroxyethyl methacrylate (HEMA) is achieved using atom transfer radical polymerization in methanol/water mixtures or pure methanol at 20 °C. The evolution of molecular weight with conversion is linear; polydispersities are around 1.1 for polymerization in methanol and around 1.2-1.3 for syntheses in 50:50 methanol/water mixtures, indicating good living character.

Surface-initiated atom transfer radical polymerization (ATRP) of various hydrophilic methacrylate monomers on submicrometer-sized silica particles in aqueous media at 20 °C leads to polymer-grafted silica particles whose colloid stability depends on the nature of the grafted polymer. These new organic−inorganic hybrid particles have been extensively characterized by thermogravimetry, elemental microanalyses, FT-IR spectroscopy, dynamic light scattering, scanning electron microscopy, and X-ray photoelectron spectroscopy. They are expected to be interesting model colloids for evaluating theories of steric stabilization.

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...

Abstract. The ionic plasma produced by a hypervelocity particle impact can be analysed to determine compositional information for the original particle by using a time-of-flight mass spectrometer. Such methods have been adopted on interplanetary dust detectors to perform in-situ analyses of encountered grains, for example, the Cassini Cosmic Dust Analyser (CDA). In order to more fully understand the data returned by such instruments, it is necessary to study their response to impacts in the laboratory. Accordingly, data are shown here for the mass spectra of ionic plasmas, produced through the acceleration of microparticles via a 2 MV van de Graaff accelerator and their impact on a dimensionally correct CDA model with a rhodium target. The microparticle dusts examined have three different chemical compositions: metal (iron), organic (polypyrrole and polystyrene latex) and mineral (aluminosilicate clay). These microparticles have mean diameters in the range 0.1 to 1.6 µm and their velocities range from 1-50 km s −1 . They thus cover a wide range of compositions, sizes and speeds expected for dust particles encountered by spacecraft in the Solar System. The advent of new low-density, microparticles with highly controllable attributes (composition, size) has enabled a number of new investigations in this area. The key is the use of a conducting polymer, either as the particle itself or as a thin overlayer on organic (or inorganic) core particles. This conductive coating permits efficient electrostatic charging and acceleration. Here, we examine how the projectile's chemical composition influences the ionic plasma produced after the hypervelocity impact. This study thus extends our understanding of impact plasma formation and detection. The ionization yield normalized to particle mass was found to depend on impact speed to the power (3.4 ± 0.1) for iron and (2.9 ± 0.1) for polypyrrole coated polystyrene and aluminosilicate clay. The ioization signal rise time was found to fall for all projectile materials from a few microseconds at low impact speeds (3 km s −1 ) to a few tenths of a microsecond at higher speeds (approximately 16 km s −1 for aluminosilicate particles and approximately 28 km s −1 for iron and polystyrene particles). At speeds greater than these the rise time was a constant few tenths of a microsecond independent of impact speed. The mass resolution of the time of flight spectrometer was found to be non-linear at high masses above 100 amu. It was ∆m/m = 5 for m = 1 amu and 40 for m = 200 amu. However, although at high masses most mass peaks had the resolution quoted, there were also occasional much narrower mass peaks observed, suggesting that at 250 to 280 amu ∆m/m = 80 to 100. The lower resolutions may be due to closely spaced mass peak signals effectively merging into one observed peak due to the (greater but still finite) resolution found for the isolated mass peaks. Complex mass spectra have been reproducibly obtained from a number of different projectiles that display many charged molecular fragm...

Recent progress in the synthesis, characterization, and applications of conducting polymer–coated latexes is reviewed.

Polypyrrole (PPy) has been deposited from aqueous solution onto two types of near-monodisperse poly(alkyl methacrylate) latexes and the resulting composite particles have been extensively characterized using SEM, DCP, XPS, FTIR, and electrical conductivity measurements. Poly(methyl methacrylate) (PMMA) latex is more difficult to coat than the polystyrene latexes previously reported by our group in that the deposited PPy overlayer is much less uniform. This difference is most likely related to the greater hydrophilicity of the PMMA surface. The poly(n-butyl methacrylate) (PBMA) latex has intermediate hydrophobic character, and, as a result, PPy overlayers on this substrate are somewhat more uniform than those obtained for PMMA particles. The PPy-coated PBMA latex is an interesting model system for understanding the behavior of PPy-coated film-forming latexes such as DSM's ConQuest (PPy-coated polyurethane particles). The lightly cross-linked outer shell of PPy hinders film formation significantly but conductive films can be obtained in the presence of coalescence aids such as N-methyl pyrrolidone. This cosolvent acts as a plasticizer for the PBMA latex and allows a reasonable degree of film formation at ambient temperature.

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A series of sterically-stabilized polystyrene latex particles in the size range 0.1-5.0 µm have been coated with ultrathin (<50 nm) overlayers of either polypyrrole, polyaniline or poly(3,4-ethylenedioxythiophene). In each case the conducting polymer overlayer allows the latex particles to acquire surface charge and hence be accelerated up to hypervelocities (>1 km s-1) using a Van de Graaff accelerator. These coated latexes have two main advantages compared to the sterically-stabilized polypyrrole particles of 0.1-0.3 µm diameter reported previously. First, a wider particle size range can be accessed. Second, the particle size distributions of the coated latexes are much narrower than those of the pure polypyrrole particles reported earlier. Preliminary studies confirm that, after charging and acceleration, these conducting polymer-coated latex particles have very similar mass-velocity profiles to those reported for colloidal iron particles in the hypervelocity literature. The hypervelocity impact generated ionization has been measured for latex spheres impacting copper targets. This is compared to previous work for impact ionization by iron particles, thus demonstrating the ability to study the dependence of impact ionization on widely different projectile materials.