A highly efficient methodology for the preparation of N-methoxycarbazoles and the total synthesis of 3,3'-[oxybis(methylene)]bis(9-methoxy-9H-carbazole)

A convenient and highly efficient method is described for the synthesis of N-methoxycarbazole derivatives, including those with sterically demanding, benzannulated, or strongly electron-donating or -withdrawing substituents. Various N-methoxycarbazole derivatives were directly prepared in good-to-moderate yields by the Pd₂(dba)₃CHCl₃/9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene-catalyzed reactions of the corresponding dibromobiphenyl compounds and methoxya-mine. Based on this methodology, the first total synthesis of 3,3′-[oxybis(methylene)]bis(9-methoxy-9H-carbazole), an antimicrobial dimeric carbazole alkaloid previously isolated from the stem bark of Murraya koenigii, was achieved in 18% yield over seven steps from 1,2-dibromobenzene.     

Phosphonitrilic chloride: 30. Synthesis of chelating polymers from cyclophosphazene derivatives and studies of their electrical conductivity and thermal properties

Chelating polymers containing copper, nickel and cobalt have been formed by reaction of the cyclophosphazene derivatives P₃N₃(NCSNHC₆H₅)₆ or P₃N₃(NCSNHNHC₆H₅)₆ and the corresponding metal ions. The polymers prepared are amorphous solids and insoluble in most organic solvents. The electrical conductivity of the products range from 8.8 × 10⁹ to 1.8 × 10¹⁴ θ-cm. The products are more stable than the corresponding ligand compounds.     

Visible light photocatalysis on praseodymium(III)-nitrate-modified TiO2 prepared by an ultrasound method

Nanocrystalline TiO₂ incorporated with praseodymium(III) nitrate has been prepared by an ultrasound method in a sol–gel process. The prepared sample is characterized by X-ray diffraction (XRD), nitrogen adsorption (BET surface area), UV–vis diffuse reflectance spectroscopy (UV–Vis DRS) and X-ray photoelectron spectroscopy (XPS). The prepared material consists of TiO₂ nanocrystalline with 5 nm size incorporated with highly dispersed Pr(NO₃)₃. Visible light absorptions at 444, 469, 482 and 590 nm are observed in the prepared sample. These bands are attributed to the 4f transitions ³H₄ → ³P₂, ³H₄ → ³P₁, ³H₄ → ³P₀ and ³H₄ → ¹D₂ of praseodymium(III) ions, respectively. This sample Pr(NO₃)₃-TiO₂, as a novel visible light photocatalyst, shows high activity and stability in the decomposing rhodamine-B (RhB) and 4-chlorophenol (4-CP) under visible light irradiation. Results examined by electron spin resonance spectroscopy (ESR) reveal that the irradiation (>420 nm) of the photocatalyst dispersed in RhB aqueous solution induces the generation of highly active hydroxyl radicals (OH), leading to the cleavage of the whole conjugated chromophore structure of RhB. A mechanism based on local excitation of praseodymium(III) nitrate chromophore and interfacial charge transfer from the chromophore to TiO₂ is proposed to explain the formation of active hydroxyl radicals in the photocatalytic system under visible light irradiation.     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Effect of post-synthesis hydrothermal treatments on the adsorptive volume of surfactant-templated mesostructures

Ordered aluminosilicate mesostructures of the MCM-41 family having a SiO₂/Al₂O₃ ratio5 were prepared using cetyltrimethylammonium chloride. These mesophases were subsequently exposed to a hydrothermal treatment (110°C for one week at autogeneous pressure). The effects of the hydrothermal treatment were documented by analyzing the samples before and after the treatments by scanning electron microscopy, N₂ sorption for pore volume and pore sizes, powder X-ray diffraction and solid-state, magic-angle-spinning (MAS)-NMR spectroscopy for the ²⁷Al and ²⁹Si nuclei. The post-synthesis hydrothermal treatment increased the mesostructure adsorptive volume by as much as 55% in mesostructures prepared from Na-aluminate (from 0.29 to 0.45 ml/g) and 27% in mesostructures prepared from Al-hydroxide (from 0.44 to 0.56 ml/g) while the average pore diameter remained essentially unchanged.

The post-synthesis hydrothermal treatment caused only small changes in the SiO₂/Al₂O₃ ratio when the source of the aluminum ion was Al-hydroxide (6.4–6.6) and Na-aluminate (5.6–5.8). The crystal symmetry did not change after successive treatments, the unit cell size of the samples prepared from Al-hydroxide increased slightly (5.5–5.7 nm) and the peak width at mid-height changed very little. The mesophases prepared from either source of aluminum showed tetrahedral (T_d) symmetry, as confirmed by ²⁷Al-MAS NMR before the hydrothermal treatment. After two successive hydrothermal treatments, almost all the Al ions show T_d symmetry together with a small population of Al ions in the octahedral (O_h) symmetry. The calcined mesostructures all showed Al ions in T_d and O_h environments.     

Synthesis and properties of tetrathiafulvalene-porphyrin assemblies

Two donor-σ-acceptor molecular systems incorporating tetrathiafulvalene (TTF) and tetraphenylporphyrin (TPP) units, TTF-TPP (dyad 1) and TTF-TPP-TTF (triad 2), were synthesized. Both dyad 1 and triad 2 and their synthetic intermediates have been characterized by ¹H nuclear magnetic resonance (¹H NMR) and mass spectrography (MS). Their ultraviolet and visible spectroscopy (UV-Vis) and cyclic voltammetry (CV) showed negligible intramolecular charge transfer interaction in their ground states. Their fluorescence intensity was strongly quenched compared with TPP, which implied the photoinduced electron transfer occurred from the TTF unit to the TPP unit in the excited state. On the other hand, their fluorescence intensity could be modulated by sequential oxidation of the TTF unit using chemical methods, which exhibited their potential application in fluorescence molecular switch.     

Development of new catalysts for N2O-decomposition from adipic acid plant

Direct decomposition of N₂O was investigated using simulated and real industrial gas stream coming from an adipic acid plant. Two different kinds of catalysts were studied: (i) LaB_1−xB′_xO₃ and CaB_1−xCu_xO₃ (B = Mn, Fe and B′ = Cu, Ni) perovskites (PVKs) and (ii) supported PVKs (10 or 20 wt.%) on γ-Al₂O₃ and CeO₂–ZrO₂. The structural modifications induced by the composition of PVK samples affect the catalytic performances: mixed oxide formation in CaMn_0.7Cu_0.3O₃ samples allows to reach the highest values of N₂O conversion while the effect of PVK phases is more controversial. The importance of copper on catalytic activities is confirmed by the investigation on CaMn_1−xCu_xO₃ samples. The best results were obtained with a CaMn_0.6Cu_0.4O₃ catalyst calcined at 700 °C for 5 h, in which the presence of copper maximises the Ca₃CuMnO₆ phase formation. The increase in Cu-content produces a large segregation of CuO despite PVK formation. The best catalyst was tested using industrial gas stream, showing good stability also in the presence of H₂O and O₂ (8% v/v ) after 1400 h on-stream. To increase surface area, Cu-containing PVKs were deposed on γ-Al₂O₃ and CeO₂–ZrO₂, and this latter has been recognised as the best support. Indeed, the activity of the PVKs supported on ceria–zirconia is comparable to and even better than that of the bulk catalysts. A possible explanation regards the support contribution in terms of activity and/or promotion of O₂ mobility which enhances the overall activity of the catalyst.     

La(H2O)3+10在蒙脱石(001)表面吸附的密度泛函计算

为研究蒙脱石(001)面与水合稀土离子La(H₂O)³⁺₁₀的相互作用对La(H₂O)³⁺₁₀在蒙脱石表面吸附的影响,分别计算了蒙脱石Na-(001)面(存在钠离子的面)和None-(001)面(不存在钠离子的面)与La(H₂O)³⁺₁₀相互作用的吸附能,距离最近的各原子的分态密度、电子转移以及作用强度。结果表明,存在Na离子的Na-(001)面吸附能更大,La(H₂O)³⁺₁₀在Na-(001)表面能更稳定的吸附。La(H₂O)³⁺₁₀的O_w(水合水分子中的氧原子)和Na-(001)表面的Na、None-(001)表面O_f(表层暴露出来的氧原子)和La(H₂O)³⁺₁₀的H_w(水合水分子中的氢原子) 存在一定的相互作用,La 原子转移到Na-(001)表面的电荷(0.44 e)大于None-(001)表面(0.16 e)。Na—O_w作用强度大于O_f—H_w,La(H₂O)³⁺₁₀在蒙脱石Na-(001)面的吸附强度比在None-(001)面更强,可推断层间Na离子增强了La(H₂O)³⁺₁₀在蒙脱石(001)表面的吸附强度。     

Dipole moments of copolymers in relation to the distribution of polar monomer unit sequences

A method for evaluating the dipole moments of copolymers in relation to the distribution of polar unit sequences is proposed. Experimental data on the synthesis and dipole moments of styrene-p-chlorostyrene and styrene-p-methoxystyrene copolymers were used to calculate the effective dipole moment of a polar unit in a copolymer. For this purpose, we assumed the following effective moment values for the corresponding polar unit sequences along the copolymer chains: when both of the nearest neighbours are polar, μ_PP, when one of the nearest neighbours is polar and the other is non-polar, μ_PS, and when both of the nearest neighbours are non-polar, μ_SS. The relative magnitudes of μ_SS, μ_PS and μ_PP calculated for both copolymers reflect the influence of dipole-dipole interactions on the effective dipole moment of a polar unit in a copolymer molecule.     

Thermal and catalytic decomposition of HNF and HAN liquid ionic as propellants

Binary aqueous hydroxylammonium nitrate (HAN: [NH₃OH]⁺[NO₃]⁻) and hydrazinium nitroformate (HNF: [N₂H₅]⁺[C(NO₂)₃]⁻) have been prepared, then thermally and catalytically decomposed. The HAN solutions were prepared with different concentrations (20, 40, 79 wt.%), whereas HNF solution contains is 40 wt.% due to its lower solubility limit (about 50 wt.%). The catalyst was prepared by impregnation of modified support (Si-modified alumina) with monometallic active phase precursor (platinum) and characterized by transmission electron microscopy, X-ray diffraction and chemisorption. The reactions were followed by thermal analysis and by using a constant volume batch reactor. This work shows the essential effect of the monopropellant concentration to determine the best formulation for an industrial application. Moreover, HAN laboratory made solutions are more efficient for catalytic decomposition due to the absence of stabilizer to inhibit the catalyst. The Pt(10%)/Al₂O₃Si + HAN_79% lab association shows lower decomposition temperatures (down to room temperature), larger reaction rates and leads to higher amount of gaseous products, giving the most efficient system. With the same catalyst, HNF solution gave lower performances than HAN solutions, suggesting that the catalyst needs to be improved for this oxidizer.     

酞菁氧钛/咔唑化合物的合成与其二阶非线性光学性能的研究

合成了具有潜在非线性光学性能的酞菁氧钛(简写为TiOPc)/咔唑化合物,用红外光谱、元素分析进行了表征,并通过实验得到了合成该化合物最佳工艺条件:n(TiOPc-SO2Cl)∶n(咔唑)=1∶1 5,反应温度150℃,反应时间为240min时,产率达到75 2%。采用溶剂化变色法估算了其二阶非线性光学性能。结果表明,其二阶非线性光学系数与基态偶极距的复合量βCTμg的值为33 9×10-30esu.D。     

聚醚砜超临界CO2发泡行为研究

以超临界CO₂为发泡剂,采用间歇发泡法制备了聚醚砜（PES）泡沫。采用旋转流变仪和扫描电子显微镜分析表征了PES发泡的均相成核行为,继而分别以滑石粉和二氧化硅（SiO₂）作为异相成核剂,探究了PES发泡过程中的异相成核行为。结果表明,间歇发泡法制备PES泡沫的发泡区间为200~230 ℃;最佳浸泡压力为20 MPa;最佳浸泡时间为3 h;未改性PES的泡孔直径均可在10 μm以下,泡孔密度在10⁹~10¹⁰ 个/cm³之间,但泡孔壁较厚;SiO₂相对于Talc,表现出更显著的异相成核作用;在210 ℃、3 h、20 MPa的发泡条件下,添加0.9 %（质量分数,下同）的SiO₂,可得到泡孔直径为0.77 μm,泡孔密度为7.14×10¹¹ 个/cm³的PES微孔泡沫。     

Co2+掺杂ZnO-MgO-Al2O3-SiO2系微晶玻璃的制备及光学性能

本文采用熔融法和热处理制备了Co²⁺掺杂的ZnO-MgO-Al₂O₃-SiO₂(ZMAS)系透明微晶玻璃,基于X射线衍射的结果确定了微晶玻璃的主要晶相为ZnAl₂O₄/MgAl₂O₄,并且随着晶化处理时间的增加,微晶玻璃的物相构成没有发生明显变化,尖晶石相的结晶度和平均晶粒尺寸呈现先增大后减小的趋势。吸收光谱和发射光谱的结果表明Co²⁺进入了尖晶石相ZnAl₂O₄/MgAl₂O₄中,并取代了四面体位置(T_d)的Zn²⁺或Mg²⁺。随着晶化处理时间的增加,样品的吸收光谱强度和发射光谱强度均呈现先升高后降低的趋势,这与X射线衍射结果的变化趋势一致,说明可以通过控制微晶玻璃的结晶度来调控光学性能,这对制备性能优良的微晶玻璃材料具有一定的指导意义。对比了采用不同价态Co的氧化物原料制备的微晶玻璃,结果表明无论是掺杂CoO还是Co₂O₃,微晶玻璃尖晶石相中的Co元素均以Co²⁺形式存在。此外,将所制备的微晶玻璃材料在1 540 nm处的基态吸收截面(σ_gas)同Co掺杂的其他基体材料进行了对比,发现它有望作为可饱和吸收体应用于调Q激光器中。     

Polymers of carbonic acid: 13. Polymerization of cyclotrimethylenecarbonate with tin tetrahalides

Polymerizations of cyclotrimethylenecarbonate (TMC) with SnCl₄, SnBr₄ were and SnI₄ were conducted in bulk. The reaction time, the temperature and the monomer/initiator (M/I) ratio were varied, and the influence of these parameters on yields and molecular weights was investigated. Yields above 90% were obtained with all these initiators, but the highest molecular weights (M_w ≈ 1.5 × 10⁵) resulted from SnI₄-initiated polymerizations. SnI₄ has the additional advantage that the polycarbonates were free of ether groups when prepared at moderate temperatures (e.g. 60°C). In contrast, SnCl₄ and SnBr₄ cause partial decarboxylation even at 60°C, and at higher temperatures up to 20 mol% of the carbonate groups may be replaced by ether linkages. Furthermore, mechanistic studies were conducted. SnCl₄ and SnBr₄ form solid 1:2 complexes with TMC at 20–25°C. Infra-red, ¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectroscopies indicate complexation at the carbonyl oxygen. Kinetic measurements of polymerizations in solvents of different polarity suggest cationic polymerization mechanisms. In addition to CH₂---OH, CH₂Cl and CH₂Br end groups were detected by ¹H n.m.r. spectroscopy. The endgroup analyses of reaction mixtures and isolated poly(TMC) support the assumption of a cationic polymerization mechanism.     

Fe2O3掺杂对氧化锌线性电阻的影响

利用固相烧结法制备出基础配方为ZnO–A1₂O3–MgO–TiO₂–SiO₂–Fe2O3的ZnO线性电阻。研究了Fe₂O₃掺杂量对ZnO线性电阻微观结构、阻温特性和阻频特性的影响。结果表明:当Fe₂O₃掺杂量为0.75%(质量分数)时,氧化锌线性电阻的非线性系数为1.1₂,阻温系数取得–8.23×10^–3/℃,此时样品的综合性能最好。     

Luminescent properties of Eu-doped YTaO4 powders

YTaO₄:Eu³⁺ powders were synthesized by a flux method with LiCl. The use of a flux in the synthesis of M′–YTaO₄ facilitated the reaction of raw materials, leading to lowering the heating temperature, but not effective at the high firing temperature. The red emission peaks were observed around 613 nm with an excitation wavelength of 254 nm. Emission peaks were composed of two sets around 613 nm and 590 nm, which originated from ⁵D₀–⁷F₂ and ⁵D₀–⁷F₁, respectively. PL intensity of YTaO₄:Eu³⁺ prepared with a small amount of LiCl (10 wt%) significantly depended on the firing temperatures, while that with a larger amount of LiCl (40 wt%) slightly relied on firing temperatures. The highest PL intensity could be obtained at the firing conditions of 1300 °C and 10 wt% LiCl.     

Effect of macromolecular length on anisotropic scattering of light in an electric field

Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, →E has been analysed. The relative variations δV^E_v, δH^E_v, δV^E_h, δH^E_h of the scattered light components are discussed for the three values [l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [(₃ − ₁)E²/2kT] of the moment induced by the principal polarizabilities ₁ = ₂ ≠ ₃. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically.     

The elastic modulus of the poly(phosphonitrilic chloride) crystal

The Young's modulus for a crystal of poly(phosphonitrilic chloride) (poly-dichlorophosphazene) (NPCl₂)_n has been calculated using force constants derived from spectroscopy. Assuming that the molecule is a uniform helix the value of the modulus is 1.38 × 10⁹ dyne cm⁻² [dyne cm⁻² = 0.1 N m⁻²]; the result is 1.66 × 10¹⁰ dyne cm⁻² if a cis-planar structure is assumed for the molecule. Neither value is close to those obtained experimentally (1.8 × 10⁶ to 6.5 × 10⁶ dyne cm⁻²). This is because experimental values relate to the amorphous polymer whereas the calculated values are those for the crystal. There is good agreement between the values calculated for the (NPCl₂)_n crystal and those for other polymer crystals.     

Deformation and toughness of polymeric systems: 3. Influence of crosslink density

In part 1 of this series the phenomenon of a critical ligament thickness (ID_c) below which brittle polymers become ductile was investigated for polystyrene (PS). Using the thermoplastic polystyrene-poly(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) model system, it was demonstrated in part 2 of this series that the absolute value of ID_c as well as the maximum toughness (i.e. maximum strain to break) was dependent on the network density of the polymer used. In this study the toughness and ID_c of crosslinked thermosetting polymers were investigated using epoxides based on the diglycidyl ether of bisphenol A as a model system. The crosslink density (v_c) is varied between values comparable with (v_c = 9 × 10²⁵ chains m⁻³), up to values much higher than (v_c = 235 × 10²⁵ chains m⁻³), the entanglement density in the thermoplastic PS-PPE system. The maximum macroscopic toughness proportional to the strain to break (λ_macr) or given by the slow-speed fracture toughness (G_Ic) and the notched high-speed tensile toughness (G_h) of core-shell rubber-modified epoxides uniquely increases with an increasing molecular weight between crosslinks (M_c). Only by using extreme testing conditions (notched high-speed impact testing), could the ID_c of a limited range of epoxides be determined: 0.21 μm (v_c = 9 × 10²⁵ chains m⁻³) ≤ ID_c ≤ 0.29 μm (v_c = 14 × 10²⁵ chains m⁻³). Both the experimentally determined values of ID_c and the toughness of the epoxides compare well with the values determined for the entangled thermoplastic PS-PPE model system in the same range of network densities, elucidating the principal similarity of the influence of entanglements and crosslinks on the deformation processes. Good agreement was observed between the experimentally determined values of ID_c of the epoxides and the values predicted by the simple model introduced in part 2 of this series.     

The dielectric properties and optical propagation loss of c-axis oriented ZnO thin films deposited by sol–gel process

The c-axis oriented ZnO thin films were prepared on various substrates by sol–gel processes. The stability of solution was examined through solvent and stabilizer. The c-axis orientation and grain size of films were increased with increasing of heat treatment temperature. The optical propogation losses of ZnO films deposited SiO₂/Si(111) substrates were measured using end-coupling method. The losses result in the scattering of the interface of ZnO/SiO₂, and the ZnO grain. Dielectric constant and resistivity of thin films deposited on Pt/SiO₂/Si(111) substrates are, respectively, in the range of 7–13 and 1.7×10⁴9.8×10⁵Ω cm.