Showing papers on "Polystyrene published in 1992"

Luminescent Colloidal Silicon Suspensions from Porous Silicon

Abstract: A procedure for generating colloidal suspensions of Si that exhibit luminescence, attributed to quantum confinement effects, is described. Samples of n- or p-type Si that have been electrochemically etched to form porous Si can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.

Morphology development in polymer blends

Abstract: The major morphological changes during polymer blending occur during the initial softening stage. This work explains the evolution of phase morphology of polymer blends from pellets to submicron particles in a co-rotating twin-screw extruder. The extruder was opened and blend samples were taken along its length. The major phase component was extracted by means of a selective solvent so that the dispersed phase morphology could be viewed directly by using scanning electron microscopy. The two systems studied were 80:20 polystyrene/amorphous polyamide and 80:20 polystyrene/polypropylene. In both systems, the initialmorphology consisted of sheets of dispersed phase

Spinodal decomposition in thin films of a polymer blend

Abstract: Spinodal decomposition in thin films of a blend of deuterated polystyrene and poly(styrene-co-4-bromostyrene) was studied with time-of-flight--elastic-recoil detection and light microscopy. We found different demixing behavior, depending on whether the films were prepared on the oxide layer of a silicon wafer or on a chromium-plated one. On the latter surface a bilayer of the two bulk phases is formed, whereas on the oxide layer a domain structure remains. The formation of the bilayer is ascribed to the complete wetting of each surface by the corresponding, preferentially adsorbed component.

Azo polymers for reversible optical storage

Abstract: A novel series of azo polymers, copolymers and polymer blends for reversible optical storage devices are described. Various azobenzenes can be bound in the side chain or within the main chain of long chain polymers such as polyester, polystyrene and poly methacrylates with very short or no spacers to a form amorphous polymers which as a film or deposited on a transparent substrate can be used to record optical information using a linearly polarized laser beam which induces optical anisotropy in the film. The information can be erased thermally by heating above the glass transition temperature, or optically by overwriting with light polarized in a predefined zero direction or with circularly polarized light.

Thermally reversible crosslinking of polystyrene via the furan-maleimide diels-alder reaction

Abstract: Mixtures of maleimidomethylated polystyrene with difurfuryl adipate or with furfuryl alcohol-esterified poly[styrene-co-(maleic anhydride)] underwent thermally reversible Diels–Alder crosslinking. Reversal of crosslinking occurred rapidly at 150°C. The instability of the furfuryl group, however, limits the practicability of the reaction. © 1992 John Wiley & Sons, Inc.

Synthesis and characterization of monodisperse porous polymer particles

Abstract: Monodisperse porous polymer particles in the size range of 10 μm in diameter were prepared via seeded emulsion polymerization. Linear polymer (polystyrene seed) or a mixture of linear polymer and solvent or nonsolvent were used as inert diluents. The pore diameters of these porous polymer particles were on the order of 1000 A with pore volumes up to 0.9 mL/g and specific surface areas up to 200 m2/g. The physical features of the porous polymer particles depended on the diluent type and the crosslinker content, as well as the molecular weight of polymer seed particles. By varying the molecular weight of the linear polymer, monodisperse porous polymer particles with different pore size distribution could be synthesized. Polymer seed with a low degree of crosslinking instead of linear polymer could also be used to prepare monodisperse porous polymer particles with smaller pore volume and pore size.

Low surface energy polystyrene

Abstract: Styrene monomers carrying C 4 F 9 and C 8 F 17 substituents were prepared and homo- and copolymerized with styrene by radical initiation. A decrease in the T g with increasing the fraction of fluorocarbon substituents was observed. Side-chain crystallization was observed for the homopolymer containing C 8 F 17 segments. This polymer exhibited a remarkably low critical surface tension by dynamic contact angle measurements, indicating the formation of a highly ordered layer of fluorocarbon degments at the polymer surface

Synthesis and properties of uniform beads based on macroporous copolymer glycidyl methacrylate–ethylene dimethacrylate: A way to improve separation media for HPLC

Abstract: Monodisperse beads based on hydrolyzed macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) for use as size-exclusion HPLC packings were synthesized by the method of “activated” swelling of polystyrene seeds followed by a suspension polymerization of both methacrylates. Effects of the type and fraction of the swelling agent, inert porogenic solvent, and cross-linking monomer on the uniformity of the particles, extent of the specific surface area, pore volume, pore size, and pore-size distribution and chromatographic properties (size-exclusion limit and column effciency) have been investigated. Trends leading to the synthesis of macroporous particles with predesigned properties for use in size-exclusion high-performance liquid chromatography in both aqueous and organic mobile phase were studied. © 1992 John Wiley & Sons, Inc.

Selective observation of the interface of heterogeneous polycarbonate/polystyrene blends by dynamic nuclear polarization carbon-13 NMR spectroscopy

Abstract: Heterogeneous blends of [3,3' -13 C 2 ] polycarbonate and [ul-ring- 12 C 6 ] polystyrene were formed by serial film casting. The polystyrene phase of each blend was homogeneously doped with 2% by weight of a bis (diphenylene) phenylallyl free-radical complex with benzene. Proton polarization enhanced by dynamic nuclear polarization was generated in the polycarbonate phase by dipolar coupling to electrons in the polystyrene phase under 39-GHz microwave irradiation at the difference of the electron and proton Larmor frequencies

Emulsifier‐free emulsion copolymerization of styrene and sodium styrene sulfonate

Abstract: The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization.

Styrene-tert-butyl methacrylate and styrene-methacrylic acid block copolymers: synthesis and characterization

Abstract: Sequential living anionic polymerization techniques were used for synthesis of block copolymers of styrene and tert-butyl methacrylate. Cumylpotassium and naphthalene-potassium complexes served as initiators for diblock and triblock copolymers, respectively. The copolymers as well as their polystyrene block had unimodal distribution of molecular weights. Their polydispersity M w /M n was typically less than 1.1. Procedures were developed for fluorescence labeling of the copolymers at the methacrylate end of the molecule or at the beginning or the end of the polystyrene block

Monodisperse porous polymer particles: Formation of the porous structure

Abstract: Monodisperse porous styrene-divinylbenzene copolymer particles were prepared via seeded emulsion polymerization using a mixture of linear polymer (polystyrene seed) and non-solvent as inert diluent. Experimental evidence was presented to describe the mechanism of formation of porous polymer particles during the copolymerization and solvent extraction stages, in which porosity was a consequence of phase separation in the presence of diluents. Pore structure formation was investigated by changes in copolymerization kinetics, gel content, crosslinking density, particle morphology, surface area, pore volume, and pore size distribution. The process of copolymerization was presented, based on the concepts of production, agglomeration, and fixation of the interior gel microspheres of polymer particles. A portion of linear polymer used as diluent was found to participate in the network structure while the porous matrix was built-up. The influence of the removal of the linear polymer from the matrix pores during the solvent extraction process on the porous structure was also discussed.

Preparation of micron-size monodisperse polymer particles having highly crosslinked structures and vinyl groups by seeded polymerization of divinylbenzene using the dynamic swelling method

Abstract: Micron-size monodisperse polystyrene/polydivinylbenzene (PS/PDVB) composite particles having highly crosslinked structures and vinyl groups were prepared as follows. First, 1.9 μm-size monodisperse PS seed particles produced by dispersion polymerization were dispersed in ethanol/water (70/30, w/w) solution which dissolved divinylbenzene (DVB) monomer, benzoyl peroxide as an initiator and poly(vinyl alcohol) as a stabilizer. The PS seed particles were swollen with a large amount of DVB monomers to 4.3 μm in diameter while keeping good monodispersity by the dynamic swelling method, where water was slowly added, continuously, with a micro feeder into the dispersion. And then, the seeded polymerization of the absorbed DVB was carried out.

Specific Interactions and Ionic Aggregation in Miscible Blends of Nylon-6 and Zinc Sulfonated Polystyrene Ionomer

Abstract: Blends of a lightly sulfonated polystyrene (10.1 mol % sulfonation) neutralized with zinc (ZnSPS) and nylon-6 (N6) were found to be miscible over the entire compositional range. Miscibility was a coneequence of transition metal complexation between the metal sulfonate and the amide groups. Melting point depression data gave a value for the polymer-polymer interaction parameter of x = -1.3, which indicates very strong intermolecular interactions. FTIR and SAXS analyses indicated that the polyamide effectively solvated the ionic associations in the blends. (ZnSPS). Differential scanning calorimetry (DSC) was used to determine miscibility and x. Fourier transform infrared spectroscopy (FTIR) was used to characterize the local environment of the Zn sulfonate groups as a function of the blend composition. This yielded infor- mation about the specific interactions between ZnSPS and N6 as well as about the ionic associations within ZnSPS. Small-angle X-ray scattering (SAXS) was em- ployed to investigate the microstructural changes in the blends, specifically the effect on the cluster morphology. Experimental Section

Miscibility of polyamide-6 with lithium or sodium sulfonated polystyrene ionomers

Abstract: Blends [50:50 (w/w)] of polyamide-6 (PA-6) with sulfonated polystyrene ionomers (containing 9.8 mol% of functional groups) show considerable miscibility enhancement (single glass transition at some compositions) when the counterion is Li but are immiscible when the counterion is Na. Dynamic mechanical measurements show that there is an optimum composition of the blends of the lithium sulfonated ionomers (LiSPS) with PA-6 at which the simultaneous disruptions of the stiffening effects of crystallinity and of the «cluster phase» in the blends are at a maximum

Phase behavior of polymer/liquid crystal blends

Abstract: Phase diagrams for liquid crystal (LC) 4-cyano-4'-n-heptylbiphenyl (7CB)/poly(methyl methacrylate) (PMMA) and polystyrene (PS)/7CB blends were constructed from DSC and optical microscopic observations showing that 7CB was partially miscible in both PMMA and PS. The study revealed that there existed a polymer/isotropic LC two-phase state at a given composition besides the polymer/nematic LC two-phase morphology and the polymer/solid crystalline LC two-phase state.

Electrically conductive semiinterpenetrating polymer networks of poly(3-octylthiophene)

Abstract: Electrically conducting semi-IPNs were synthesized from soluble poly(3-octylthiophene), styrene monomer, and a cross-linking agent. By controlling the level of cross-linking of the polystyrene component, it was possible to create semi-IPNs with highly dispersed microdomains of the conjugated polymer. For example, semi-IPN samples containing 20% poly(3-octylthiophene) (P3OT) and 10% divinylbenzene (DVB) exhibit very finely dispersed P3OT domains on the order of 1000 A. This particular cross-linking level also produced semi-IPNs with a very low percolation threshold

Role of surfactant in composite latex particle morphology

Abstract: Composite particles were prepared by seeded emulsion polymerization at 70°C using K2S2O8 as initiator and two different nonionic surfactants. Monodisperse polystyrene latex particles were used as seed and methyl methacrylate was used as second-stage monomer. When the surfactant, polyethylene oxide–propylene oxide (Pluronic F-108), was used, the final particle morphology showed that the PMMA (core) was partially covered by polystyrene. However, when nonyphenol polyethylene oxide (Igepal Co-990) was used as surfactant, one observed a reversed type of encapsulation (i.e., PS core is partially engulfed by PMMA). The interfacial tensions of the polymer phase against water containing the appropriate surfactant were measured by the drop-volume method and used in a mathematical model based on thermodynamic analysis to predict the equilibrium particle morphology. The observed particle morphologies were found to differ from the predicted morphologies at low conversion of the second-stage monomer but agreed with it at higher conversion.

Influence of phase separation on the linear viscoelastic behavior of a miscible polymer blend

Abstract: The influence of phase separation on the linear viscoelastic response has been studied in miscible blends of polystyrene and poly(vinyl methyl ether) with a lower critical solution temperature near 110 °C. At temperatures between 25 and 155 °C, and for compositions in the range 20% to 60% polystyrene, the complex moduli G’ and G‘ were measured at frequencies in the range of 0.01 to 100 rad/s. Time–temperature superposition was applied in the single phase region to obtain the complex modulus over eight decades of frequency. Increasing the polystyrene content resulted in an increase in the zero‐shear viscosity and a shift of the terminal behavior to lower frequencies or longer times. The phase separation above the lower critical solution temperature was measured as a sudden increase in the fluorescence intensity of an anthracene‐labeled polystyrene (approximately 1 wt % in the blend), using an optical probe in the rheometer fixture. For the 20/80 and 40/60 PS/PVME samples, the terminal zone was in the acces...

Aggregation in polystyrene-sphere suspensions in near-critical binary liquid mixtures

Abstract: We study the reversible aggregation of polystyrene latex spheres (PLS) in one phase mixtures of 2,6 lutidine plus water at temperatures and solvent compositions near the solvent mixture's critical point. The aggregation occurs only on the side of the critical composition rich in the liquid component which is nonpreferred when the system is in the solvent's two-phase region. The liquid that is preferred can be changed by changing the surface charge density of the PLS. The aggregation region extends to temperatures well beyond the wetting temperature, and dynamic light scattering shows no evidence of a thick layer building up on individual particles before they join aggregates.