Thermoswitching property in TCNQ salts of ionenes containing poly(ethylene oxide) segments

Ionene polymers characterized by the alternating structure of ionene and crystalline poly(ethylene oxide) (PEO) segments were prepared as a function of PEO segment size. A microstructure of these ionenes and their 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts were investigated with x-ray diffraction patterns, thermal scanning behavior, and polarizing micrographs. On the basis of this microstructure, the change in resistivity with temperature was studied. In Arrhenius' plots of the resistivity the simple salts in which the spherulites consisting of the PEO segments were observed showed a sharp decrease in resistivity with a rise in temperature [critical temperature resistor (CTR)] at about the melting point of the PEO segments, whereas the other simple salts in which the spherulites were not observed showed linear temperature dependence. The switching properties were confirmed similarly in repetitive heating/cooling cycles. This CTR characteristic was attributed to an increase in continuity in the conduction paths by melting spherulites. The apparent switching properties were not observed in the complex salts.     

Alkane Oxidation with Molecular Oxygen Using a New Efficient Catalytic System: N-Hydroxyphthalimide (NHPI) Combined with Co(acac)(n)() (n = 2 or 3)

A novel class of catalysts for alkane oxidation with molecular oxygen was examined. N-Hydroxyphthalimide (NHPI) combined with Co(acac)(n)() (n = 2 or 3) was found to be an efficient catalytic system for the aerobic oxidation of cycloalkanes and alkylbenzenes under mild conditions. Cycloalkanes were successfully oxidized with molecular oxygen in the presence of a catalytic amount of NHPI and Co(acac)(2) in acetic acid at 100 degrees C to give the corresponding cycloalkanones and dicarboxylic acids. Alkylbenzenes were also oxidized with dioxygen using this catalytic system. For example, toluene was converted into benzoic acid in excellent yield under these conditions. Ethyl- and butylbenzenes were selectively oxidized at their alpha-positions to form the corresponding ketones, acetophenone, and 1-phenyl-1-butanone, respectively, in good yields. A key intermediate in this oxidation is believed to be the phthalimide N-oxyl radical generated from NHPI and molecular oxygen using a Co(II) species. The isotope effect (k(H)/k(D)) in the oxidation of ethylbenzene and ethylbenzene-d(10) with dioxygen using NHPI/Co(acac)(2) was 3.8.     

Catalyzed collapse and enhanced hydrogen storage of BN nanotubes

The novel morphology of BN nanotubes with a collapsed structure has been discovered by a metal-catalyzed treatment. The collapse causes the dramatic enlargement of a specific surface area of BN nanotubes and remarkably enhances the hydrogen storage capacity of BN nanotubes.     

Synthesis of poly(2-cyclohexenone-4-yl methacrylate) and acidolysis of pendant protecting groups in the polymer

4-Acetoxy-2-cyclohexenone (ACH) and 2-cyclohexenone-4-yl methacrylate (CHM) were obtained from the condensation reaction of 4-bromo-2-cyclohexenone (BCH) with acetic acid and methacrylic acid using 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU), respectively. Poly(2-cyclohexenone-4-yl methacrylate) ( P-1 ) containing acid-sensitive 2-cyclohexenone-4-yl group was prepared from the radical polymerization of CHM and the esterification of poly(methacrylic acid) with BCH using DBU. Furthermore, P-1 and CHM copolymers ( P-2 and P-3 ) were easily synthesized from the radical polymerization of methacrylic acid and comonomers in dimethylsulfoxide using 1 mol % of 2,2′-azobis (isobutyronitrile) followed by esterification of the resulting polymers with BCH using DBU by one-pot method. The deprotection reaction of ACH and P-1 was carried out in dichloromethane using an acid catalyst. The reaction proceeded smoothly in solution to give phenol and the corresponding carboxylic acid. Therefore, the 2-cyclohexenone-4-yl group is a useful protecting group for carboxylic acids, because the protection and deprotection reactions are very easy. In the case of polymer films, however, the acid was trapped by carbonyl group on the 2-cyclohexenone-4-yl group, and did not cause the deprotection reaction. © 1993 John Wiley & Sons, Inc.     

Synthesis of Ultrafine SiC Powders from Carbon-Silica Hybridized Precursors with Carbothermic Reduction

Inorganic-organic hybrid gels were prepared by simultaneous condensation of the liquid mixture of ethyl silicate, ethyl borate and water soluble phenol resin with low molecular weight. The liquid mixtures were changed into lightly colored transparent gels after a catalyst addition and stirring. The obtained gels were crushed, dried and fired in controlled conditions to yield the inorganic precursors. Since the tailored inorganic precursors mainly consisted of SiO2 and carbon, silicon carbide was formed with the heat treatments in an Ar atmosphere beyond 1773 K with carbothermic reduction. The properties and morphology of the formed silicon carbide powders in terms of the starting precursor compositions and the conditions of the carbothermic reduction were investigated with SEM, XRD and TG-DTA analysis.     

Polyimides having pendant hydroxy and acetoxy groups. I. Synthesis of polyimides from pyromellitimide and bisepoxides

Polyimides having pendant hydroxy groups were prepared by addition of pyromellitimide with bisepoxides. Tertiary amines and quaternary ammonium halides were effective as a catalyst. The polyimides were soluble in dichloroacetic acid and had inherent viscosities in the range 0.16–0.19 dl/g. Thermogravimetric analysis showed that a rapid weight loss of the polymers occurred at about 400°C. The pendant hydroxy groups were easily acetylated by treating the polymers with a mixture of acetic anhydride and pyridine. The acetylated polyimides were soluble in dimethylformamide, dimethylacetamide, and dioxane and melted at 120–150°C.     

Layer-by-layer assembled multilayer films of titanate nanotubes, Ag- or Au-loaded nanotubes, and nanotubes/nanosheets with polycations

Aqueous suspensions of hydrothermally synthesized titanate nanotubes and poly(diallyldimethylammonium chloride) (PDDA) have been employed to fabricate multilayer films on various substrates in a layer-by-layer fashion. Atomic force microscopy displays the dense coverage of the substrate surface by the nanotubes. UV-vis absorption spectroscopy confirms the consecutive growth of PDDA/nanotube layer pairs. Single crystalline Ag and Au nanoparticles with narrow size distribution spatially correlating with the nanotubes have been obtained by treating the nanotubes with AgNO(3) or HAuCl(4) aqueous solution followed by chemical reduction. The noble metal nanoparticles show a strong surface plasmon absorption band. A multilayer film construction of the noble-metal-loaded nanotubes has also been achieved. This process has been further extended to the heteroassembly of nanotubes/nanosheets in different layer sequences.     

Synthetic studies on oxindole spiro-lactones with thalliumd(III) trinitrate: A formal total synthesis of (±)-tryptoquivaline G

(±)-Tryptoquivaline G was formally synthesized through shortened steps from tryptophan, in which oxidation with thallium(III) trinitrate(TTN) was effected at the crucial stage. The present work also constitutes the first synthesis of oxindole lactones carrying 2-alkyl quinazolinones.     

Optically active 2-p-tolylsulfinylacrylate a novel chiral dienophile which exhibits high reactivity and diastereoselectivity

The Diels-Alder reaction of a novel chiral dienophile, alkyl ($\text{S}$)-2-$\text{p}$-tolylsulfinylacrylates 1 with anthracene and cyclopentadiene showed high diastereoselectivity under the chelation controlled condition.     

Selective desorption and analysis of humic substances on suspended particles in river water

The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes.