Showing papers on "Polystyrene published in 2002"

Dispersion of Functionalized Carbon Nanotubes in Polystyrene

Abstract: Polystyrene nanocomposites with functionalized single-walled carbon nanotubes (SWNTs), prepared by the in-situ generation and reaction of organic diazonium compounds, were characterized using melt-state linear dynamic viscoelastic measurements. These were contrasted to the properties of polystyrene composites prepared with unfunctionalized SWNTs at similar loadings. The functionalized nanocomposites demonstrated a percolated SWNT network structure at concentrations of 1 vol % SWNT, while the unfunctionalized SWNT-based composites at twice the loading of SWNT exhibited viscoelastic behavior comparable to that of the unfilled polymer. This formation of the SWNT network structure for the functionalized SWNT-based composites is because of the improved compatibility between the SWNTs and the polymer matrix and the resulting better dispersion of the SWNT.

Ordered nanoporous polymers from polystyrene-polylactide block copolymers.

Abstract: Nanoporous polystyrene monoliths were prepared from polystyrene−polylactide (PS−PLA) block copolymers that form hexagonally packed nanocylinders of PLA in a PS matrix. A morphology diagram was developed to determine the range in composition and molecular weight over which this morphology existed. Macroscopic alignment of these materials gave anisotropic monoliths that were subjected to mild degradation conditions leading to the chemical etching of the PLA. The resulting nanoporous monoliths consisted of a polystyrene matrix containing hexagonally close-packed, oriented, and continuous nanoscopic channels (pore size was tunable through synthesis or blending) lined with chemically accessible hydroxyl functional groups. Both the precursors and the porous materials were analyzed moleculary (size-exclusion chromatography and proton nuclear magnetic resonance spectroscopy) and structurally (small-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry). In addition, the surfa...

Functionalization of Carbon Nanotubes with Polystyrene

Abstract: Single-walled and multiple-walled carbon nanotubes were functionalized with a polystyrene copolymer, poly(styrene-co-p-(4-(4‘-vinylphenyl)-3-oxabutanol)). The functionalization reaction conditions ...

Atom Transfer Radical Polymerization Synthesis and Magnetic Characterization of MnFe2O4/Polystyrene Core/Shell Nanoparticles

Abstract: An atom transfer radical polymerization route is developed for the coating of MnFe2O4 nanoparticles with polystyrene yielding the core−shell nanoparticles with size <15 nm. Magnetic studies show a decrease in coercivity after the formation of polystyrene shell, which is considered due to the reduction of magnetic surface anisotropy upon polymer coating. The MnFe2O4 nanoparticles as the magnetic core were separately prepared by a reverse micelle microemulsion method. Polymerization initiators are chemically attached onto the surface of nanoparticles. The modified nanoparticles are then used as macro-initiators in the subsequent polymerization reaction. This approach provides great flexibility in the selection of magnetic core. Consequently, magnetic tunability is able to be introduced into these core/shell nanoparticulate systems to achieve the desired superparamagnetic response.

SWNT-Filled Thermoplastic and Elastomeric Composites Prepared by Miniemulsion Polymerization

Abstract: SWNT-filled polystyrene (SWNT-PS) and styrene−isoprene (SWNT-SI) composites prepared by miniemulsion polymerization showed distinctive physical features such as uniform black coloration, high solubility in toluene as well as in tetrahydrofuran (THF), and semiconductor to ohmic electrical behavior. Raman spectra for both hybrid materials suggested a reduced vibrational freedom of the polymer chains as a consequence of the nanotube incorporation. An adsorbed polymer layer on the nanotube bundles contributes to a better dispersion of the inorganic nanoreinforcement.

Thermal conductivity of polystyrene–aluminum nitride composite

Abstract: The thermal conductivity of polymer composites having a matrix of polystyrene (PS) containing aluminum nitride (AlN) reinforcement has been investigated under a special dispersion state of filler in the composites: aluminum nitride filler particles surrounding polystyrene matrix particles. Data for the thermal conductivity of the composites are discussed as a function of composition parameters (aluminum nitride concentration, polystyrene particle size) and temperature. It is found that the thermal conductivity of composites is higher for a polystyrene particle size of 2 mm than that for a particle size of 0.15 mm. The thermal conductivity of the composite is five times that of pure polystyrene at about 20% volume fraction of AlN for the composite containing 2 mm polystyrene particle size. The relationship between thermal conductivity of composites and AlN filler concentrations has been compared with the predictions of two theoretical models from the literature.

SiOH-Functionalized Polystyrene Latexes. A Step toward the Synthesis of Hollow Silica Nanoparticles

Abstract: Following a previous work (Tissot, I.; Lefebvre, F.; Bourgeat-Lami, E. Macromolecules 2001, submitted for publication), polystyrene latex particles containing silanol groups have been synthesized in emulsion polymerization using 3-(trimethoxysilyl)propyl methacrylate (MPS) as a functional comonomer. The surface properties of the functionalized polymer latexes were investigated in depth using electrophoretic measurements and the soap titration method. Both techniques gave qualitative evidence of the presence of SiOH groups at the particles surface. The concentration of surface charges was quantified by potentiometric and conductometric titrations. As expected, the surface charge density increased with an increase in the pH and with an increase in the MPS concentration. Because of the presence of silanol groups at the particles surface, no loss of colloidal stability was observed when the functional polystyrene latexes were suspended into ethanol/water mixtures. The silanol groups were then converted into a...

Star polymer synthesis using trithiocarbonate functional β-cyclodextrin cores (reversible addition–fragmentation chain-transfer polymerization)

Abstract: Polystyrene stars were synthesized with reversible addition-fragmentation chain-transfer (RAFT) polymerization. The core of the stars comprised a trithiocarbonate heptafunctional beta-cyclodextrin ring. Polymerizations were performed at 100 and 120 degreesC in the absence of an extraneous initiator and at 60 degreesC in the presence of a radical initiator. Monofunctional trithiocarbonate was also synthesized and used to make linear polystyrene to allow direct a comparison with the star synthesis. In all cases, the polymerization kinetics conformed to pseudo-first-order behavior. The measured molecular weights of the stars were found to deviate from those predicted on the basis of the monomer/trithiocarbonate group ratio. The extent of this deviation was dependent on the polymerization temperature, RAFT agent concentration, and conversion. Despite the low radical concentrations, termination reactions are suggested to play a significant role in the seven-arm polystyrene star syntheses. The synthetic method was found to be suitable for generating star block structures. (C) 2002 Wiley Periodicals, Inc.

Reversible Redox Cleavage/Coupling of Polystyrene with Disulfide or Thiol Groups Prepared by Atom Transfer Radical Polymerization

Abstract: Polymers with chemically labile disulfide groups in the backbone were prepared by atom transfer radical polymerization (ATRP) of styrene using the 2-bromopropionic acid diester of bis(2-hydroxyethyl) disulfide as the initiator and CuBr/N,N,N‘,N‘ ‘,N‘ ‘-pentamethyldiethylenetriamine as the catalyst at 90 °C. Polymerization kinetics indicated insignificant transfer to the disulfide originating from the initiator. Using a monomer-to-initiator-to-catalyst ratio of 300:1:0.2, radical coupling reactions were suppressed compared to systems with more catalyst (300:1:1), and well-defined (with symmetrical and narrow (Mw/Mn < 1.1) molecular weight distribution) disulfide-containing polymers were prepared. The internal disulfide bond was cleaved by reduction with dithiothreitol to yield the corresponding thiol-terminated polystyrene. The thiol end groups were efficiently coupled back to the starting disulfide by oxidation with FeCl3. A dibromo-terminated polystyrene was synthesized under similar ATRP conditions usin...

Magnetic Nanocomposites: Preparation and Characterization of Polymer-Coated Iron Nanoparticles

Abstract: Nanoparticles bearing a strongly bound polymer coating were formed by the thermal decomposition of iron pentacarbonyl in the presence of ammonia and polymeric dispersants. The dispersants consist of polyisobutylene, polyethylene, or polystyrene chains functionalized with tetraethylenepentamine, a short polyethyleneimine chain. Polystyrene-based dispersants were prepared with both graft and block copolymer architectures. Inorganic−organic core−shell nanoparticles were formed with all three types of dispersants. In addition, more complex particles were observed in the case of the polystyrene-based dispersants in 1-methylnaphthalene. The core material was identified as metallic iron, while the particle shells are formed from the polymeric dispersant which binds to the core. High-resolution TEM revealed evidence for crystallization within the polymer shell, possibly facilitated by chain alignment upon binding. The nanocomposites display room-temperature magnetic behavior ranging from superparamagnetic to ferr...

Synthesis of silver nanodisks using polystyrene mesospheres as templates

Abstract: We report the synthesis of Ag nanodisk using polystyrene mesospheres as templates. TEM measurements show that the average disk thickness is 9.0 ± 1.0 nm and the diameter is 36 ± 8 nm. The particles...

Solvent-induced crystallization of syndiotactic polystyrene: Thermodynamics and morphology

Abstract: The thermodynamic properties and the morphology of syndiotactic polystyrene solid samples exposed to solvents (benzene and toluene) are investigated. It is shown that, as far as the melting propert...

Synthesis of Adaptive Polymer Brushes via “Grafting To” Approach from Melt

Abstract: We report a simple method to synthesize binary polymer brushes from two incompatible polymers of different polarity. The synthetic route is based on a subsequent step-by-step grafting of carboxyl-terminated polystyrene and poly(2-vinylpyridine) to the surface of a Si wafer functionalized with 3-glycidoxypropyl-trimethoxysilane. The end-functional polymers were spin-coated on the substrate, and grafting was carried out at a temperature higher than the glass transition temperature of the polymers. The composition of the binary brushes can be regulated based on grafting kinetics of the first polymer by the change of time or/and temperature of grafting. This method reveals a smooth and homogeneous polymer film on the macroscopic scale, while at the nanoscopic scale the system undergoes phase segregation effecting switching/adaptive properties of the film. Upon exposure to different solvents, the film morphology reversibly switches from “ripple” to “dimple” structures as well as the surface energetic state swi...

Syntheses of raspberrylike silica/polystyrene materials

Abstract: Raspberrylike hybrid organic−inorganic materials consisting of spherical silica beads supporting smaller polystyrene particles were prepared through a heterophase polymerization process. In a first step, micrometer-sized silica particles were synthesized according to procedures inspired from the literature. In a second step, a poly(ethylene glycol) macromonomer was adsorbed on the surface of the silica beads. Finally, polymerization of styrene was achieved in water with a nonionic surfactant as an emulsifying agent and sodium persulfate as an initiator. Scanning and transmission electron microscopies show that the presence of the macromonomer on the surface of the silica particles is a determining parameter in order to get the raspberrylike morphology.

Resin composition for toner and toner

Abstract: A resin composition for toners which comprises a vinyl copolymer obtained mainly from a styrene monomer and a (meth)acrylic ester monomer, a Fischer/Tropsch wax, and a polystyrene block copolymer, characterized in that the vinyl copolymer has a molecular weight distribution as determined by gel permeation chromatography in which at least two peaks are present respectively in the molecular-weight region of from 5,000 to 20,000 and the region of molecular weights not lower than 500,000, that the wax is contained in an amount of 2 to 10 wt.%, and that the block copolymer is contained in an amount of 0.5 to 5 wt.%; and a toner containing the resin composition.

Synthesis and rheology of intercalated polystyrene/Na+-montmorillonite nanocomposites

Abstract: Polystyrene (PS)/clay nanocomposites were synthesized by the emulsion polymerization of styrene in the presence of sodium ion-exchanged montmorillonite (Na+-MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers. The nanocomposites were examined by means of X-ray diffraction, transmission electron microscopy, thermogravimetric analysis. The rheological properties of the PS/Na+-MMT nanocomposites were also studied to exhibit more pronounced shear thinning behavior with increasing clay content.

Synthesis, Characterization, and Nonlinear Optical Properties of Hybridized CdS−Polystyrene Nanocomposites

Abstract: Hybrid composites of CdS nanoparticles embedded in sulfonated polystyrene (PS) matrixes have been prepared and characterized. The −SO3- groups acted as the coordination sites for cadmium ion aggregations and nanosized CdS particles were successfully grown in situ at these sites with the release of S2- ions from thioacetamide. The density and size of the nanoparticles were found to be a function of the sulfonate content of PS and the concentration of Cd2+ feed ions used. Ionic clusterings within the polymer matrix occurred at a sulfonate content of 9.9 mol % and has provided a confined medium for particle growth in uniform size. The optical properties of the prepared CdS−PS hybrid composites were characterized by linear absorption and fluorescence spectra. Z-scan measurement was also employed to investigate the nonlinear optical properties at a wavelength of 532 nm. The results showed that the nonlinear refractive index of the composite varies with the input irradiance, thus indicating not just third-order...

Synthesis and characterization of silica‐graft‐polystyrene hybrid nanoparticles: Effect of constraint on the glass‐transition temperature of spherical polymer brushes

Abstract: The effect of the chain constraint on the glass-transition temperature of polystyrene (pS) was studied in the context of polymer tethering to curved surfaces. The synthesis and characterization of silica-graft-polystyrene (SiO2-g-pS) hybrid nanoparticles is reported. Silica nanoparticles possessing covalently bound pS chains were prepared by the atom transfer radical polymerization of styrene from functionalized colloidal surfaces. These hybrid nanoparticles serve as interesting examples of spherical polymer brushes, as a high density of grafted pS was achieved on the inorganic colloid. The confirmation of a brushlike extension of immobilized chains in a good solvent was obtained with dynamic light scattering in toluene of SiO2-g-pS colloids possessing various molar masses of tethered pS. The solid-state morphology of SiO2-g-pS ultrathin films was assessed with transmission electron microscopy, and this confirmed that the silica colloids were well-dispersed in a matrix of the tethered polymer. Differential scanning calorimetry was used to study the effects of tethering and chain immobilization on the glass-transition temperature of pS. The measured glass-transition temperature of annealed bulk films of the hybrid nanoparticles was elevated with respect to the value for pure bulk pS. The enhancements ranged from 13 to 2 K for SiO2-g-pS brushes possessing tethered pS with number-average molecular weights of 5230 and 32,670 g/mol, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2667–2676, 2002

Synthesis of polymer–montmorillonite nanocomposites by in situ intercalative polymerization

Abstract: Two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium- and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline-MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer-MMT nanocomposites.

Organic secondary ion mass spectrometry: sensitivity enhancement by gold deposition.

Abstract: Hydrocarbon oligomers, high-molecular-weight polymers, and polymer additives have been covered with 2-60 nmol of gold/cm2 in order to enhance the ionization efficiency for static secondary ion mass spectrometry (s-SIMS) measurements. Au-cationized molecules (up to -3,000 Da) and fragments (up to the trimer) are observed in the positive mass spectra of metallized polystyrene (PS) oligomer films. Beyond 3,000 Da, the entanglement of polymer chains prevents the ejection of intact molecules from a "thick" organic film. This mass limit can be overcome by embedding the polymer chains in a low-molecular-weight matix. The diffusion of organic molecules over the metal surfaces is also demonstrated for short PS oligomers. In the case of high-molecular-weight polymers (polyethylene, polypropylene, PS) and polymer additives (Irganox 1010, Irgafos 168), the metallization procedure induces a dramatic increase of the fingerprint fragment ion yields as well as the formation of new Aucationized species that can be used for chemical diagnostics. In comparison with the deposition of submonolayers of organic molecules on metallic surfaces, metal evaporation onto organic samples provides a comparable sensitivity enhancement. The distinct advantage of the metal evaporation procedure is that it can be used for any kind of organic sample, irrespective of thickness, opening new perspectives for "real world" sample analysis and chemical imaging by s-SIMS.

Preparation and Characterization of Core−Shell Particles Containing Perfluoroalkyl Acrylate in the Shell

Abstract: We describe the preparation and characterization of core−shell latex particles, consisting of a polystyrene core, covered with a perfluoroalkyl acrylate shell. The core−shell particles were prepared by a two-stage emulsion polymerization under kinetically controlled conditions and were characterized by transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The surface properties of the latex films produced from the core−shell particles were investigated by the contact angle method. Compared with random copolymers or latex blends of styrene and perfluoroalkyl acrylate, the core−shell particles were the most effective to reduce the surface energy of the latex films. The effect of acetone as a cosolvent on the polymerization process was also considered.

Fabrication of Hollow Polystyrene Nanospheres in Microemulsion Polymerization Using Triblock Copolymers

Abstract: A ternary microemulsion polymerization was successfully used to prepare nanosized hollow polystyrene (PS) microlatexes with triblock copolymers of poly(oxyethyene)−poly(oxypropylene)−poly(oxyethylene)[(EO)x(PO)y(EO)x] Micelle formation using triblock copolymers is a useful nanoreactor in order to make polymer nanoparticles in oil/water (o/w) microemulsions Poly(methyl methacrylate)/cross-linked polystyrene core/shell nanospheres have been fabricated by o/w microemulsion PS hollow nanospheres were obtained using the polymer core etching technique Water-soluble and oil-soluble initiators were used for the polymerization at 70 °C with moderate stirring and via modified buret feeding After extraction of the surfactant matrix, the polymer particles contract considerably without the change of their spherical shape The hollow sphere morphology and hollow image of the polymer particles were confirmed by field emission scanning electron microscope and transmission electron microscope PS hollow spheres were

Multiblock Copolymers in the Compatibilization of Polystyrene and Poly(methyl methacrylate) Blends: Role of Polymer Architecture

Abstract: An asymmetric double cantilever beam (ADCB) was utilized to determine the ability of a series of styrene and methyl methacrylate copolymers with varying architectures to compatibilize the polystyrene/poly(methyl methacrylate) interface. Diblock, triblock, pentablock, and heptablock multiblock copolymers with similar molecular weights were compared to a random copolymer. When the surface is saturated with copolymer, PS/PMMA interfaces compatibilized with pentablock copolymers [S−M−S−M−S(30) and M−S−M−S−M(30)] were the strongest, followed by triblock [S−M−S(50) and M−S−M(50)] and then diblock [S−M(100)]. The least blocky structures, heptablocks [S−M−S−M-S−M−S(21) and M−S−M−S−M−S(21)] and random, provided the weakest interfaces under similar conditions. The ability of the multiblock copolymers to strengthen the PS/PMMA interfaces was attributed to multiple interface crossings and blocks of monomers that are able to anchor into the homopolymers. The results suggest that block lengths with molecular weight gre...

Using adhesion to probe viscoelasticity of polymer film surfaces: a quartz crystal microbalance study.

Abstract: We have used a quartz crystal microbalance to monitor the adhesion of small particles to the surface of polystyrene films. This technique is shown to provide a signature of viscoelastic relaxation processes at the polymer surface. For M n values less than 104 and greater than 105, this signature occurs at a temperature ∼ 12.5 K above the measured bulk glass transition temperature, T g. For intermediate values of M n however, the relaxation signature occurs at temperatures as low as 7 K above the bulk T g. This observation suggests a slight decrease in the T g value near the polymer surface. A model incorporating the effects of enrichment of polymer chain ends at the free surface was considered and found to provide a quantitative description of the data.

Silicalite-1 Hollow Spheres and Bodies with a Regular System of Macrocavities

Abstract: Silicalite-1 macrostructures in the form of hollow silicalite-1 spheres and bodies with a regular system of macrocavities were prepared using two types of polystyrene beads as shape-directing macrotemplates. The incompatibility between the organic support and the inorganic shell was circumscribed by using negatively charged substrates, reverse of their surface charge, and adsorption of zeolite nanoseeds. These pretreated microbeads were subsequently subjected to a continuous growth in a zeolite precursor mixture. The combustion of the polystyrene core leads to the transformation of the core/shell beads into hollow silicalite-1 spheres. The mechanical properties of the latter were found to be a function of the thickness of the silicalite-1 shell, the diameter-to-wall thickness (d:t) ratio, and the calcination conditions. Silicalite-1 bodies with a regular system of macrocavities were prepared by hydrothermal treatment with a silicalite-1 precursor mixture of a layer of pretreated polystyrene beads deposite...