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971.
Hollow poly(divinylbenzene-co-methacrylic acid) (P(DVB-co-MAA)) microspheres were prepared by the selective dissolution of the non-crosslinked poly(methacrylic acid) (PMAA) mid-layer in ethanol from the corresponding silica/PMAA/P(DVB-co-MAA) tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid (MAA) via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica core, which was prepared by the Stöber hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene (DVB) crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). 相似文献
972.
Conceptual density functional theory is exploited to understand the reactivity in a medium of solvents with increasing dielectric constants. Aprotic as well as protic solvents are used for this study. It is found that the global parameters, such as chemical potential and hardness, decrease from gas phase to solvent phase with increasing dielectric constant. However, it is observed that the Fukui functions of the reactive atoms increase significantly with the dielectric constants of the aprotic solvents while for the protic solvents the variation of the reactivity indices is insignificant. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
973.
Ortensia Ilaria Parisi Francesco Puoci Francesca Iemma Giuseppina De Luca Manuela Curcio Giuseppe Cirillo Umile Gianfranco Spizzirri Nevio Picci 《先进技术聚合物》2010,21(11):774-779
A novel, simple synthetic strategy for the preparation of crosslinked polymers with significant antioxidant properties is proposed. Ferulic acid (FA), a well‐known antioxidant compound, due to its reactivity toward free radical process, was inserted into a polymeric network with methacrylic acid (MAA) and ethylene glycole dimethacrylate acting as comonomer and crosslinker, respectively. All the reactants were simultaneously mixed in the polymerization feed and one‐pot radical reaction was carried out. Irregular microparticles were prepared by bulk polymerization and microspheres by precipitation polymerization. The materials were characterized by nuclear magnetic resonance–magic angle spinning (NMR‐MAS) studies, to verify effective FA insertion into polymeric networks, and by morphological, dimensional analyses, and water absorption measurement to study their superficial and swelling properties, respectively. Antioxidant properties of materials were evaluated by linoleic acid emulsion system–thiocyanate assay, determination of scavenging activity on DPPH radicals, determination of available phenolic groups in polymeric matrices, and determination of total antioxidant capacity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
974.
La-doped HfO2 gate dielectric thin films have been deposited on Si substrates using La(acac)3 and Hf(acac)4 (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO2 films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO2 films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm2 at Vg = 1V + Vfb. MOCVD-derived La-doped HfO2 is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications. 相似文献
975.
The article describes the microstructure and morphological properties of microwave dielectric ceramic thin films. These thin films were successfully prepared on SiO2 (1 1 0) single-crystal substrates by radio frequency magnetron-sputtering system. The microstructure and morphology of the thin films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The results show that the main phase is Ba0.5Sr0.5Nb2O6,which has a tetragonal perovskite structure, a long strip pattern, and uniform crystal-grain size of about 2-3 μm in length when annealed under 1150 °C for 30 min in an O2 atmosphere. These thin films are of excellent crystallization quality, with a polycrystalline and dense structure. 相似文献
976.
Bimodal mesoporous TiO2 microspheres with high photocatalytic activity were prepared by a hydrothermal method using titanium sulfate as precursor in the presence of urea. The results indicate that all prepared samples show bimodal pore-size distributions in the mesoporous region: smaller intra-aggregated pores with peak pore diameter of ca. 2 nm and larger inter-aggregated pores with peak pore diameter of ca. 12.5 nm. The molar ratio of urea to Ti(SO4)2 (Ru) has an obvious influence on the morphology, microstructure and photocatalytic activity of TiO2. With increasing Ru, specific surface areas and porosity increase, contrarily, the crystallite size and relative anatase crystallinity decrease. The photocatalytic activity first increases with Ru. At Ru = 2.0, the photocatalytic activity reaches the highest and is obviously higher than that of Degussa P25. With further increasing Ru, the photocatalytic activity decreases. The formation rate of hydroxyl radicals during photocatalysis has a positive correlation with the photocatalytic activity. 相似文献
977.
Szigeti Z Malon A Vigassy T Csokai V Grün A Wygladacz K Ye N Xu C Chebny VJ Bitter I Rathore R Bakker E Pretsch E 《Analytica chimica acta》2006,572(1):1-10
Ten Ag+-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag+ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10−11 M (potentiometrically) and 2 × 10−11 M Ag+ (optically) are found with bridged thiacalixarenes. 相似文献
978.
Summary: Synthesis, properties and medical diagnostic applications of hydrophilic nano- and microspheres with carboxyl, aldehyde and hydroxyl groups on their surface are described. The particles were obtained by emulsion copolymerization of styrene, acrolein, methyl methacrylate, methacrylic acid, and 2-hydroxyethyl methacrylate carried on in water media and initiated with potassium persulfate. Stabilization of particles' suspensions was provided by addition of sodium dodecyl sulfate to polymerizing mixture or by formation of surfactants in situ in copolymerization involving acrolein or α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer (PGL). Relations between interfacial properties of these particles and their ability for covalent immobilization of proteins, with eliminated or at least reduced nonspecific adsorption of these species were investigated. The particles with covalently attached proteins (antigens or antibodies) were used for preparation of diagnostic tests based on visual or turbidimetric observation of particles' aggregation or by monitoring changes in their electrophoretic mobility accompanying specific antigen (or antibody) binding. The later test was directed toward determination of antibodies against Helicobacter pylori. Principle of a new type of diagnostic test based on photonic crystals of microspheres are described. 相似文献
979.
Polyimides incorporating the ferrocene unit were prepared by in situ curing of poly (amic acid) macromolecules with ferrocene, for the molecular-level design of low dielectric constant (low-κ) materials. The effects of ferrocene on dielectric properties of polyimide are investigated in detail in this study. Ferrocene containing polyimides exhibit a number of desirable properties including low-water absorption and admirable thermal stability. Systematic studies demonstrate that proper insertion of ferrocene into a polyimide backbone can give rise to a reduction in the material's dielectric constant. All composites were subjected to DSC measurements for the purpose of examining Tg from all composition. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and the other conventional techniques were used for structural characterization. 相似文献
980.
Etienne Gaudin Bernard Chevalier Wilfried Hermes Ute Ch. Rodewald Rainer Poettgen 《ChemInform》2009,40(41):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献