Silyl Triflate-Initiated Ring-Opening Polymerizations of Cyclosiloxanes

Polymer yields between 70 and 85% form in ring-opening polymerizations of trimeric cyclosiloxanes initiated with trimethylsilyl triflate in the presence of a selective scavenger for protic acids, 2,6-di-t-butylpyridine. Examples include the polymerization of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (F₃) and hexamethylcyclotrisiloxane (D₃). Siloxane bond redistribution is essentially absent and data are presented establishing a nonterminating polymerization giving an average of roughly one trimethylsilyl group per chain. The present observations contrast with other work that suggests that the presence of free triflic acid is required for initiation with trimethylsilyl triflate.     

Shape-selective isopropylation of biphenyl over a highly dealuminated mordenite: effect of propylene pressure

A highly dealuminated H-mordenite (H-M) catalyzed the selective isopropylation of biphenyl to 4,4-diisopropylbiphenyl (4,4-DIPB). The high selectivity is ascribed to the shape-selective catalysis in mordenite pores. The selectivity of 4,4-DIPB decreased during the isopropylation of biphenyl due to isomerization of 4,4-DIPB under low propylene pressure. The increase of propylene pressure suppressed the isomerization in the isopropylation. 4,4-DIPB itself was isomerized over highly dealuminated H-M under low propylene pressure.     

Synthesis and properties of aromatic polyesters and brominated polyesters derived from α,α′-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene

The interfacial polycondensation technique was used for the preparation of polyarylates and brominated polyarylates. Polyarylates and brominated polyarylates were prepared by mixing a solution of diacid chloride such as terephthaloyl chloride, isophthaloyl chloride, or their mixture in dichloromethane with an aqueous alkaline solution of ,-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene or ,-bis(4-hydroxy-3,5-dibromophenyl)-1,4(or 1,3)-diisopropylbenzene using triethylbenzylammonium chloride as the phase transfer agent. Moderate to high molecular weight polyarylates with _inh up to 1.27 dL/g were obtained, and most of them could be cast into tough and flexible films depending on the polymer composition. In general, polymers containing more 1,3-isomer or isophthaloyl chloride moieties gave transparent and flexible films and had lower glass transition temperatures and higher solubility. Although these polymers have two isopropylidene linkages in their repeating units, they still exhibit moderately high thermal stability and show no obvious weight loss before 400 °C. The introduction of bromine on the polymer backbone caused a decrease of inherent viscosity, crystallinity, and thermal stability of the polyarylates, while causing an increase in glass transition temperature and a great enhancement of fire retardancy.     

Shape-Selective Alkylation of Biphenyl over H-[Al]-SSZ-31 with Propylene

Isopropylation of biphenyl (BP) over [Al]-SSZ-31, a large-pore, one-dimensional zeolite has been studied. Effects of temperature, pressure and SiO₂/Al₂O₃ ratio were examined. SSZ-31 was found to be an active catalyst in the isopropylation of biphenyl with propylene. The selectivity for 4-isopropylbiphenyl (4-IPBP) and 4,4-diisopropylbiphenyl (4,4-DIPB) was high among isopropylbiphenyl (IPBP) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating SSZ-31 shows shape-selective catalysis. The selectivity for 4,4-DIPB decreased with temperature increase; correspondingly the selectivity for thermodynamically more stable isomers (3,3- and 3,4 DIPB) increased with temperature. The yield of IPBP isomers decreased while that of DIPB isomers increased with temperature increase. Pressure showed less effect on conversion; however, increase in pressure suppresses the isomerization of 4,4-DIPB to 3,3- and 3,4-DIPB. Conversion decreased with increase in SiO₂/Al₂O₃ ratio. At low SiO₂/Al₂O₃ ratio of 136, relatively high triisopropylbiphenyl (TriIPB) isomers were formed in bulk products and their amount decreased with increase in SiO₂/Al₂O₃ ratio.     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Electrosynthesis of 4,4′-dinitroazobenzene on PbO2 electrodes

Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO₂ electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO₂ electrode. It was found that the electrocatalytic activity of a PbO₂ electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.     

High-Performance Directional Metallopolyamides. II. Optical Spectroscopic Studies of Metal Chelation

The chelating interaction between metal ions and 4,4-disubstituted-2,2-bipyridyl-containing high-performance polymeric ligands prepared from 2,2-bipyridyl-4,4-dicarboxylic acid and a series of primary aromatic diamines was investigated by optical spectroscopy. Optical spectroscopic studies of the chelation of ruthenium ions by the 2,2-bipyridyl-containing polyamides revealed the formation of distinct ruthenium(II) complexes [Ru^II(poly)L₄] ( _max=530 nm), [Ru^II(poly)₂L₂] ( _max=584 nm), and [Ru^II(poly)₃]²⁺ ( _max=476 nm), while iron(II) ions formed only one complex ( _max=569 nm). The diverse functional features of the polymer repeat unit directly influences the chelation of metal ions.     

High-Performance Directional Metallopolyamides. I. Synthesis and Thermal Analysis

High-performance polyamides containing the 4,4-disubstituted-2,2-bipyridyl moiety were synthesized by phosphorylation polycondensation from 2,2-bipyridyl-4,4-dicarboxylic acid and a series of primary aromatic diamines with triphenylphosphite and pyridine as the agents to facilitate condensation. Polyamides exhibiting improved solubility in organic solvents and strong acids, melting transitions at low temperatures, and good thermal properties were prepared by introducing bulking methyl and fluoro groups and flexible ether and propyl linkages and by using monomers with reduced symmetry. Solutions of the polyamides with rigid main chains (III, IV, V, VI, and VIII) showed birefringence (colorful spherulites) at concentrations of 5, 10, and 15% (w/v) polymer/solvent. The chelation of ruthenium(II) ions resulted in the preparation of directional metallopolyamide systems based on the geometrically favorable tris(2,2-bipyridyl)ruthenium(II) complex. The three-dimensional polyamides, which absorbed at a _max of 476 mm and emitted at a _max of 620 nm, exhibited a high thermal stability and improved solubility, making them suitable candidates for compressive strength studies and cyclic voltammetry studies as part of an effort to address the corrosion of graphite fiber-reinforced composites.     

Ammonia synthesis over multi‐promoted iron catalysts obtained by high‐energy ball‐milling

The feasibility of producing ammonia synthesis catalysts from highenergy ballmilling of a simple mixture of the constituent oxides has been investigated. The effect of ballmilling the fused oxidic precursor of the industrial KM1 ammonia synthesis catalyst has also been studied. The results show that highenergy ballmilling offers some interesting possibilities for preparing novel catalytic materials. It is observed that ballmilling of the powder oxides mixture leads to formation of solid solutions and the catalytic activity is significantly higher than that of the starting material. Furthermore, ballmilling of fused oxidic KM1 precursor is seen to give rise to more homogeneous promoter distribution and slightly higher activity. The quite small activity increase observed in this case probably reflects the fact that the fusion process has already resulted in a close to optimal promoter distribution. The choice of atmosphere during ballmilling is also seen to offer possibilities for regulating the phase composition.     

Factors governing the electrochemical synthesis of α-nickel (ii) hydroxide

The electrodeposition of -nickel hydroxide is promoted by the simultaneous chemical corrosion of the electrode by an acidic nitrate bath. Chemical corrosion results in the formation of a poorly ordered layered phase which is structurally similar to -nickel hydroxide and provides nucleation sites for the deposition of the latter. Therefore under conditions which enhance corrosion rates such as low current density (<1.3 mA cm–2), high temperature (60 C), high nickel nitrate concentration ( 1M) and the resultant low pH (1.7), -nickel hydroxide electrodeposition is observed, while -nickel hydroxide forms under other conditions. Further, -nickel hydroxide deposition is more facile on an iron electrode compared to nickel or platinum.     

Preparation of Linear π-Conjugated Coordination Polymers Having Ruthenium(II) Complex in the Main Chain

Soluble -conjugated coordination polymers having a ruthenium(II) complex in the main chain were prepared from a soluble metal complex monomer and a bridging ligand via coordination. Refluxing of an ethanol-water suspension containing (4,4-dinonyl-2,2-bipyridyl)Ru(III) with 2,3-bis(2-pyridyl)pyrazine gave the coordination polymer. The resulting polymer was soluble in common organic solvents. The structure was confirmed by uv/vis spectra and gpc analysis.     

A miscibility study of ternary blends of polystyrene,tetramethylbisphenol-A polycarbonate,and poly(2,6-dimethyl-1,4-phenylene oxide)

Phase behaviorof ternary blends of polystyrene (PS), tetramethylbisphenol-A polycarbonate (TMPC), and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at two different temperatures (i.e., 210 and 300 °C, respectively) was studied by means of differential scanning calorimetry. Miscibility of the ternary blends at either temperature was found restricted to limited compositions, in agreement with simulated spinodal curves based on published values of interaction parameters. The limited ability of PS, which is separately miscible with TMPC and PPO at 210 °C, to act as a common solvent for the immiscible TMPC/PPO pair at this temperature was explained in terms of the disparity in PS/TMPC and PS/PPO pair interactions (i.e., the 'X effect).     

Experimental Study of Ignition of a Gasoline–Air Mixture in a Constant‐Volume Combustion Chamber

The characteristics of flamekernel development in a premixed gasoline–air mixture in a cylindrical constantvolume combustion chamber are measured. The experiments are performed with an initial temperature of 393 K, pressure of 6 bar, and equivalence ratio = 0.8 with the use of various ignition systems and spark plugs. The schlieren pictures of the process are presented, and the measured results for flame velocity, heatrelease rate, and mass fraction of the burnt fuel are analyzed.     

Localization of Deformation in Copper Single Crystals During Explosive Collapse

It is established that highrate axisymmetric loading of single crystals by the method of explosive collapse of a hollow thickwalled cylinder causes deformation that involves all active closepacked slip systems. The spatial distribution of macroscopic sites of strain localization is determined by the crystallography of the active systems in singlecrystalline samples. The established correlation between the observed shear bands in the microstructure of copper single crystals and {111} active slip <110> systems of facecentered cubic (FCC) crystals and their symmetric arrangement show that deformation at a rate of 5 · 10⁴ sec^-1 occurs according to the crystalline structure of the materials.     

A highly active palladium complex catalyst in the synthesis of N,N′-diphenylurea from nitrobenzene,aniline and carbon monoxide

A catalyst system comprising palladium acetate and bidentate bis(diphenylphosphino)alkane ligand of general formula Ph₂P(CH₂)_nPPh₂ (n = 3–5) was highly active in N,N-diphenylurea synthesis from nitrobenzene, aniline and carbon monoxide and showed different reactivity from the system with the more common monodentate triphenylphosphine ligand.     

Liquid Phase Selective Benzoylation of Chlorobenzene to 4,4′-Dichlorobenzophenone over Zeolite H-Beta

Selective formation of 4,4-dichlorobenzophenone (>88%) at 19.8 wt% conversion level of 4-chlorobenzoylchloride (4-ClBC) and at 8.4×10^–4 s^–1mol^–1 _Al turnover frequency (TOF) of 4-chlorobenzoylchloride is reported for the first time in the benzoylation of chlorobenzene using 4-ClBC as benzoylating agent and zeolite H-beta as the catalyst.     

Synthesis, Characterization and Optimum Reaction Conditions of Oligo-N, N′-bis (2-hydroxy-1-naphthalidene) Thiosemicarbazone

The oxidative polycondenzation reaction conditions of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (HNTSC) using air oxygen, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 50–90°C. Oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was characterized by ¹H-NMR, FT-IR, UV-Vis, size exclusion chromatography (SEC) and elemental analysis techniques. Solubility testing of oligomer was investigated using organic solvents such as DMF, THF, DMSO, methanol, ethanol, CHCl₃, CCl₄, toluene acetonitrile, ethyl acetate, concentrated H₂SO₄ and an aqueous alkaline solution. Using NaOCl, H₂O₂ and air O₂ oxidants, conversion to oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (OHNTSC) of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was found to be 85, 80 and 76%, respectively, in an aqueous alkaline medium. According to the SEC analyses, the number-average molecular weight, weight-average molecular weight and polydispersity index values of OHNTSC synthesized were found to be 1050 gmol^–1 1715 gmol^–1 and 1.63, using NaOCl, and 2137, 2957 gmol^–1 and 1.38, using air O₂ and 2155 gmol^–1 4164 gmol^–1 and 1.93, using air H₂O₂, respectively. Also, TG analysis was shown to be unstable of oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone against thermo-oxidative decomposition. The weight loss of OHNTSC was found to be 97.29% at 900°C.     

Catalytic Methoxycarbonylation of Aromatic Diamines with Dimethyl Carbonate to Their Dicarbamates Using Zinc Acetate

The methoxycarbonylation of 2,4-toluene diamine and 4,4-diphenylmethane diamine with dimethyl carbonate to the corresponding dicarbamates using zinc acetate was carried out at 453 K. Zn(OAc)₂, prepared by evacuating Zn(OAc)₂2H₂O at 383 K for 2 h, yields dimethyltoluene-2,4-dicarbamate in 96% yield in 2 h, while Zn(OAc)₂2H₂O yields dimethyl-4,4-methylenediphenyldicarbamate in 98% yield at 453 K in 2 h.The structure of methyl 3-amino-4-methyl phenyl carbamate, which is one of the intermediates for the reaction of 2,4-toluene diamine with dimethyl carbonate into dimethyltoluene-2,4-dicarbamate, has been determined by measuring the NOE spectrum of ¹H NMR.     

Partial oxidation of methane to synthesis gas

Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (92%) is obtained with a 421 N₂CH₄O₂ ratio at 1050 K and atmospheric pressure, with a space velocity of 4×10⁴ hour^–1.     

Asymmetric structure analysis of active surface-sites by in situ polarized total-reflection fluorescence EXAFS

An in situ polarization-dependent total reflection fluorescence yield EXAFS system has been developed to analyze the asymmetric structures of catalytically active metal sites on single crystal surfaces. This technique separately reveals the bonding feature parallel and perpendicular to the support surface. The systems of Cu ion on -quartz(0001), Co oxide on -alumina(0001), and Pt₄ on -alumina(0001) were investigated as model surfaces of supported catalytic systems. The location of Cu sites on -quartz(0001), the epitaxial growth mode of Co₃O₄ on -alumina(0001), and the Pt raft structure with metal-support interaction in Pt₄ / -alumina(0001) were observed.