Polymerization of styrene with diphenylzinc-cocatalyst systems

Summary The diphenylzinc-H₂O and diphenylzinc-H₂O-Bu^tCl systems were used as catalysts for styrene polymerization in solution at various temperatures and solvents. The systems are greatly influenced by the molar ratio H₂O/Ph₂Zn, and the maximum catalyst activity, in both cases, was found at a molar ratio of 0.75. GPC results strongly suggest the presence of more than one active species. For Ph₂Zn-H₂O-Bu^tCl system, in dichloromethane at-78°C with the molar ratio of H₂O/Ph₂Zn=0.75, the reaction is first order with respect to monomer with k_p=2.45×10^-3 Lmol^-1sec^-1.     

Polymerization of styrene with diphenylzinc-butanone systems

Summary In the present work we report the results of the polymerization of styrene using diphenylzinc-butanone, Ph₂Zn-MeCOEt. Our results indicate that these systems induce the polymerization of styrene reaching a larger conversion when the molar ratio MeCOEt/Ph₂Zn=1,0. According to size exclusion chromatography, SEC, studies of the polystyrene obtained using the Ph₂Zn-MeCOEt showed unimodal curves and have molecular weight distribution narrower than those obtained using the Ph₂Zn-H₂O system, suggesting a more simple reaction system.Partly presented at the 2nd Brazillian Polymer Conference, Sao Paulo, Brasil, October 1993     

Synthesis of vicinal diamines via Zn–H2O–CO2-induced reduction of aromatic imines in supercritical carbon dioxide

Zn–H₂O–CO₂ is a good reducing reagent for the reduction of imines in supercritical carbon dioxide (scCO₂). They provide the corresponding vicinal diamines in moderate to good yields. The results showed that carbon dioxide plays an important role as both solvent and reagent.     

Electrodeposition and characterization of Zn–Ni alloys as sublayers for epoxy coating deposition

The chemical composition and phase structure of Zn–Ni alloys obtained by electrodeposition under various conditions were investigated. The influence of the deposition solution and deposition current density on the composition, phase structure, current efficiency and corrosion properties of Zn–Ni alloys were examined. It was shown that the chemical composition and phase structure affect the anticorrosive properties of Zn–Ni alloys. A Zn–Ni alloy electrodeposited from a chloride solution at 20 mA cm^–2 exhibited the best corrosion properties, so this alloy was chosen for further examination. Epoxy coatings were formed by cathodic electrodeposition of an epoxy resin on steel and steel modified with a Zn–Ni alloy. From the time dependence of the pore resistance, coating capacitance and relative permittivity of the epoxy coating, the diffusion coefficient of water through the epoxy coating, D(H₂O), and its thermal stability, it was shown that the Zn–Ni sublayer significantly affects the electrochemical and transport properties, as well as the thermal stability of epoxy coatings. On the basis of the experimental results it can be concluded that modification of a steel surface by a Zn–Ni alloy improves the corrosion protection of epoxy coatings.     

Ph<Subscript>2</Subscript>Zn-metallocene-MAO initiator systems in the homo- and copolymerization of styrene/<Emphasis Type="Italic">p</Emphasis>-alkylstyrene

Summary The homo- and copolymerization of styrene (S) with p-methylstyrene (p-MeS) and p-tert-butylstyrene (p-Bu^tS) has been tested using initiator systems of the Ph₂Zn-metallocene-MAO type. The metallocenes used were CpTiCl₃, IndTiCI₃, (n-BuCp)₂TiCl₂, Ind₂ZrCl₂ and Et(Ind)₂ZrCl₂. The Ph₂Zn-metallocene-MAO systems homopolymerize styrene, p-methylstyrene and p-tert-butylstyrene, producing syndiotactic polymers in the case of the titanocenes and amorphous polymers in the case of the zirconocenes. The S/p-MeS and S/p-Bu^tS copolymers obtained with the Ph₂Zn-titanocene-MAO systems are enriched in the comonomer with respect to the initial feed.     

Estimates of the interannual variations of N2O emissions from agricultural soils in Canada

The DNDC model was used to estimate direct N₂O emissions from agricultural soils in Canada from 1970 to 1999. Simulations were carried out for three soil textures in seven soil groups, with two to four crop rotations within each soil group. Over the 30-year period, the average annual N₂O emission from agricultural soils in Canada was found to be 39.9 Gg N₂O–N, with a range from 20.0 to 77.0 Gg N₂O–N, and a general trend towards increasing N₂O emissions over time. The larger emissions are attributed to an increase in N-fertilizer application and perhaps to a trend in higher daily minimum temperatures. Annual estimates of N₂O emissions were variable, depending on timing of rainfall events and timing and duration of spring thaw events. We estimate, using DNDC, that emissions of N₂O in eastern Canada (Atlantic Provinces, Quebec, Ontario) were approximately 36% of the total emissions in Canada, though the area cropped represents 19% of the total. Over the 30-year period, the eastern Gleysolic soils had the largest average annual emissions of 2.47 kg N₂O–N ha^–1 y^–1 and soils of the dryer western Brown Chernozem had the smallest average emission of 0.54 kg N₂O–N ha^–1 y^–1. On average, for the seven soil groups, N₂O emissions during spring thaw were approximately 30% of total annual emissions. The average N₂O emissions estimates from 1990 to 1999 compared well with estimates for 1996 using the IPCC methodology, but unlike the IPCC methodology our modeling approach provides annual variations in N₂O emissions based on climatic differences.     

Thermodynamics of hydrobromic acid in t-butanol + water mixtures from electromotive force measurements

The standard potentials of AgAgBr electrode have been determined in eighteen t-butanol + water mixtures containing up to 90 wt% t-butanol from the emf measurements of the cell Pt, H₂ (g, 1 atm): HBr (m), X% Bu^tOH, Y% H₂O: AgBr, Ag at nine different temperatures from 15 to 55°C at five intervals. The standard molal potential in each solvent has been expressed as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr, and the standard thermodynamic quantities for the transfer of one mole of HBr from water to t-butanol + water media have been computed and discussed.     

Preferential CO oxidation in H2-rich gas mixtures over Au/doped ceria catalysts

Nanosized gold catalysts supported on doped ceria were prepared by deposition–precipitation method. A deep characterization study by HRTEM/EDS, XRD, FT-Raman, TPR and FTIR was undergone in order to investigate the effect of ceria modification by various cations (Sm³⁺, La³⁺ and Zn²⁺) on structural and redox properties of gold catalysts. Doping of ceria affected in different way catalytic activity towards purification of H₂ via preferential CO oxidation. The following activity order was observed: Au/Zn–CeO₂ > Au/Sm–CeO₂ > Au/CeO₂ > Au/La–CeO₂. The differences in CO oxidation rates were ascribed to different concentration of metallic gold particles on the surface of Au catalysts (as confirmed by the intensity of the band at 2103 cm⁻¹ in the FTIR spectra collected during CO–O₂ interaction). Gold catalysts on modified ceria showed improved tolerance towards the presence of CO₂ and H₂O in the PROX feed. The spectroscopic experiments evidence enhanced reactivity when PROX is performed in the presence of H₂O already at 90 K.     

Preparation of alkaline PVA-based polymer electrolytes for Ni–MH and Zn–air batteries

Alkaline PVA polymer electrolyte with high ionic conductivity of about 0.047 S cm^–1 at room temperature was obtained by a solution casting method. The PVA polymer electrolytes, blended with KOH and H₂O, were studied by DSC, TGA, cyclic voltammetric and a.c. impedance methods. The PVA polymer electrolytes show good mechanical strength and high ionic conductivity. The electrochemical stability window at the metal–electrolyte interface is ±1.2 V for stainless steel. Ni–MH and Zn–air batteries with PVA polymer electrolytes were assembled and tested. Experimental results show good electrochemical performances of the PVA-based Ni–MH and Zn–air batteries.     

Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media

Two methods were used to remove Cr(VI) from industrial wastewater. Although both are based in the same general reaction: 3Fe(II)_(aq) + Cr(VI)_(aq) ; 3Fe(III)_(aq) + Cr(III)_(aq) the way in which the required amount of Fe(II) is added to the wastewater is different for each method. In the chemical method, Fe(II)_(aq) is supplied by dissolving FeSO₄ · 7(H₂O)_(s) into the wastewater, while in the electrochemical process Fe(II)_(aq) ions are formed directly in solution by anodic dissolution of an steel electrode. After this reduction process, the resulting Cr(III)_(aq) and Fe(III)_(aq) ions are precipitated as insoluble hydroxide species, in both cases, changing the pH (i.e., adding Ca(OH)_2(s)). Based on the chemical and thermodynamic characteristics of the systems Cr(VI)–Cr(III)–H₂O–e^– and Fe(III)–Fe(II)–H₂O–e^– both processes were optimized. However we show that the electrochemical option, apart from providing a better form of control, generates significantly less sludge as compared with the chemical process. Furthermore, it is also shown that sludge ageing promotes the formation of soluble polynuclear species of Cr(III). Therefore, it is recommended to separate the chromium and iron-bearing phases once they are formed. We propose the optimum hydraulic conditions for the continuous reduction of Cr(VI) present in the aqueous media treated in a plug-flow reactor.     

Electrodeposition and characterization of thin layers of Zn–Co alloys obtained from glycinate baths

An alkaline bath containing CoSO₄ · 7H₂O, ZnSO₄ · 7H₂O, Na₂SO₄ and NH₂CH₂COOH is proposed for the deposition of thin layers of Zn–Co alloys onto steel substrates. Electrodeposition was carried out at 0.216–1.080 A dm^–2, pH 10 and 10–55 °C. The influence of bath composition, current density and temperature on galvanostatic cathodic polarization, cathodic current efficiency and alloy composition was studied. Different proportions of the two metals were obtained by using different deposition parameters, but at all Zn(II)/Co(II) ratios studied, preferential deposition of zinc occurred and anomalous codeposition took place. Increasing the bath temperature enhanced the cobalt content in the deposit. X-ray diffraction measurements indicated that the phase structure of the deposits was controlled by the applied current density. The Co₅Zn₂₁ phase was formed at low current density, while the CoZn₁₃ phase was formed at high current density. The potentiodynamic dissolution of the coatings showed that they contained Zn–Co alloy of different content and structure.     

Homopolymerization of styrenic monomers and their copolymerization with ethylene using group 4 non-metallocene catalysts

Homopolymerization of styrenic monomers (St, p-Me-St, p-tBu-St, p-tBuO-St) and their copolymerization with ethylene, with the use of [(^tBu2O₂NN′)ZrCl]₂(μ-O) ( 1 ) and (^tBu2O₂NN′)TiCl₂ ( 2 ), where ^tBu2O₂NN′ = Me₂N(CH₂)₂N(CH₂-2-O⁻-3,5-tBu₂-C₆H₂)₂, is explored in the presence of MMAO and (iBu)₃Al/Ph₃CB(C₆F₅)₄. The ethylene/styrenic monomers copolymerization with 1 /MMAO produces exclusively copolymers with high activity and good comonomer incorporation whereas the other catalytic systems yield mixtures of copolymers and homopolymers. The use of p-alkyl styrene derivatives instead of styrene raises the catalytic activity, comonomer incorporation and molecular weights of the copolymers. Complex 2 exhibits higher activity in homopolymerization of styrenic monomers than 1 irrespective of the kind of the activator employed. A clear dependence is observed for the molecular weight and catalyst activity against the kind of the styrenic monomer. The obtained polymers were atactic and only the complex 2 , when activated by MMAO, promoted the highly syndiospecific polymerization of p-Me-St and p-tBu-St. Poly(p-tBuO-St) exhibits fiber-forming properties.     

Ethylene/α‐olefin copolymerization by nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) dichloride/AliBu3/Ph3CB(C6F5)4 catalyst systems

A series of nonbridged (cyclopentadienyl) (aryloxy)titanium(IV) complexes of the type, (η⁵‐Cp′)(OAr)TiCl₂ [OAr = O‐2,4,6‐^tBu₃C₆H₂ and Cp′ = Me₅C₅ ( 1 ), Me₄PhC₅ ( 2 ), and 1,2‐Ph₂‐4‐MeC₅H₂ ( 3 )], were prepared and used for the copolymerization of ethylene with α‐olefins (e.g., 1‐hexene, 1‐octene, and 1‐octadecene) in presence of AlⁱBu₃ and Ph₃CB(C₆F₅)₄ (TIBA/B). The effect of the catalyst structure, comonomer, and reaction conditions on the catalytic activity, comonomer incorporation, and molecular weight of the produced copolymers was examined. The substituents on the cyclopentadienyl group of the ligand in 1 – 3 play an important role in the catalytic activity and comonomer incorporation. The 1 /TIBA/B catalyst system exhibits the highest catalytic activity, while the 3 /TIBA/B catalyst system yields copolymers with the highest comonomer incorporation under the same conditions. The reactivity ratio product values are smaller than those by ordinary metallocene type, which indicates that the copolymerization of ethylene with 1‐hexene, 1‐octene, and 1‐octadecene by the 1–3/ TIBA/B catalyst systems does not proceed in a random manner. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrochemical characteristics and structural changes of molybdenum trioxide hydrates as cathode materials for lithium batteries

Several characteristics of MoO₃·2H₂O and MoO₃·H₂O, such as thermal behaviour and conductivity and the electrochemical behaviour and structural changes associated with discharge and charge have been investigated. The suitability of these substances as new cathode materials for non-aqueous lithium batteries has been assessed. MoO₃·H₂O, having only one coordinated water molecule, showed a discharge capacity of about 400 Ah kg^–1 of acid weight and a discharge potential around 2.5 V vs Li/Li⁺. This capacity was much higher than the 280 Ah kg^–1 of anhydrous MoO₃.MoO₃·H₂O showed good charge-discharge cyclic behaviour at a capacity below l e^–/Mo while keeping the original layered lattice on cycling. In addition, the crystal system of MoO₃·H₂O was found to be changed from a monoclinic system to orthorhombic with lattice parameters ofa=0.5285 nm,b=1.0824 nm,c=0.5237 nm on discharge to 0.5 e^–/Mo.This paper was originally presented at the Fall 1987 Meeting of the Electrochemical Society, Inc. held at Honolulu, Hawaii (Proceedings of the Symposium on Primary and Secondary Ambient Temperature Batteries, PV88-6, p. 484–493 (1987).     

The effect of certain ions on the internal stress of bright copper electrodeposits

The effect of low concentrations (0–100 mg 1^–1) of F, Cl, Br, I, As, Sb, Bi, Ni, Zn, Fe, Ag, Te, Se, Pb, and S on the internal stress of bright copper electrodeposits was studied. The following solution containing 30 mg 1^–1 of thiourea as a brightening additive was used as the electrolyte: CuSO₄·5H₂O (225 g l^–1), H₂SO₄ (60g l^–1). It is shown that the internal stress of copper electrodeposits can be considerably reduced by addition of Se(IV), Cl, Br, or I to the above electrolyte.     

Effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte

The effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments. The solution chemistry of aluminium, zinc, and iron in aqueous solution in the absence and in the presence of fluoride ions was studied with the construction of the Eh-pH diagrams for the Al–F–H₂O, Zn–F–H₂O and Fe–F–H₂O systems at 25°C. In the presence of fluoride ions, aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH whereas zinc and iron can form soluble or insoluble metal-fluoride complex species only at relatively high fluoride concentration and at higher pH values. Experimental results show that in the presence of fluoride ions, the corrosion of pure aluminium in sulphuric acid is due to uniform dissolution and the reaction rate depends on the fluoride concentration. In zinc electrolyte containing fluoride ions, zinc deposits onto the pure aluminium substrate spontaneously and the amount of deposited zinc also depends on the fluoride concentration. On the other hand, the presence of iron in the Al–Fe alloy accelerates the corrosion of aluminium in H₂SO₄ and zinc electrolyte significantly and prevents the deposition of zinc on the aluminium surface. The effect of fluoride ions on zinc adherence to the aluminium is also discussed.     

Ferrite process of electroplating sludge and enrichment of copper by hydrothermal reaction

In this paper, ferrite process of electroplating sludge and enrichment of copper by hydrothermal reaction was investigated. By the hydrothermal treatment, Zn, Ni, Cu, Cr-bearing electroplating sludge can be transformed into high value-added Ni–Zn–Cr ferrite by adding iron source (FeCl₃·6H₂O) and precipitator. The most optimum reaction conditions were explored: 1.57 g/g dry sludge as the dosage of FeCl₃·6H₂O, pH 8.5 of the slurry adjusted by ammonia, 4 h as the reaction time, and 200 °C as the reaction temperature. Under these conditions, the purer Ni–Zn–Cr ferrite could be prepared, and Cu was extracted to the range from 76 wt% to nearly 84 wt%, when ammonia was selected as the precipitator. Leaching toxicity of heavy metals from Ni–Zn–Cr ferrite prepared with additional iron source and precipitator, was much lower than the regulated limit of Toxicity Characteristic Leaching Procedure (TCLP), indicating that Ni–Zn–Cr ferrite synthesized hydrothermally from electroplating sludge had a better chemical stability. Therefore, the ferrite process by hydrothermal reaction is a feasible method with respect to the reuse and self-purification of electroplating sludge.     

Dynamic in situ observation of automotive catalysts for emission control using X-ray absorption fine structure

Two main pivotal subjects of research in automotive catalysts were studied by modern X-ray absorption analysis techniques. One is oxygen storage/release behaviour, and the other is sintering inhibition of Pt particles. First, three types of CeO₂–ZrO₂ (Ce:Zr = 1:1 molar ratio) compounds with different oxygen storage/release capacities and different structural properties were prepared, and the valence change of Ce as a function of temperature during oxygen release/storage processes was investigated. The reduction of surface Ce mainly occurred in the range 100–170 °C, and the reduction of bulk Ce progressed at high temperatures of 170 °C and above. The Ce reduction behaviour depended not only on the homogeneity of the Ce and Zr for bulk reduction at high temperatures but also on the particle size of the CeO₂–ZrO₂ samples for surface reduction at low temperatures. Secondly, sintering inhibition of Pt in Pt/Al₂O₃, Pt/MgO and Pt/ceria-based catalysts after 800 °C ageing in air was studied. We found that the Pt–O–M (M = Mg, Ce) bond acted as an anchor and inhibited the sintering of Pt particles on MgO or ceria-based oxide. Especially, it was noteworthy that the Pt–O–Ce⁴⁺ bond on the ceria-based support breaks easily through the reduction of Ce (Ce⁴⁺ → Ce³⁺) during the usual stoichiometric and reducing conditions.     

Synthesis and Characterization of 5-Coordinate Tungsten Hydride Anions: [(tBu3SiNH)(tBu3SiN=)2HWR]M

Treatment of (^tBu₃SiNH)(^tBu₃SiN=)₂WH ( 1 -H) with small alkyl anions (RM) afforded tungsten alkyl hydride anions [(^tBu₃SiNH)(^tBu₃SiN=)₂HWR)]M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K (two isomers); R=CCH, M=Na; R=CH=CH₂ (Vy), M=Li). The saturated alkyl anions 3 -(R)M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K) degraded via apparent 1,2-RH-elimination to produce the known [(^tBu₃SiN=)₃WH]M ( 2 -HM), but the acetylide ( 3 -(C₂H)Na) and vinyl ( 3 -(Vy)Li) anions converted to their hydrogenated isomers, [(^tBu₃SiN=)₃WVy]Na ( 2 -VyNa) and [(^tBu₃SiN=)₃WEt]Li ( 2 -EtLi), respectively. The structure of 3 -(ⁿBu)Li is reported, and a discussion of tungsten-hydride coupling constants in ^tBu₃SiX-ligated (X=O, NH, N) systems is given.     

Biomimetic oxidation studies. 7. Alkane functionalization with a MMO structural model, [Fe2O(OAc)(tris((1-methylimidazol-2-yl) methyl) amine)2]3+, in the presence oft-butyl hydroperoxide and oxygen gas

A biomimetic structural model of the active site of methane monooxygenase enzyme, [Fe₂O(OAc)(tris((1-methylimidazol)-2-methyl)amine₂]³⁺, 1, has been shown to functionalize cyclohexane, toluene, adamantane, propane, and ethane in the presence oft-butyl hydroperoxide and oxygen gas. A mechanism is proposed to account for these results which implicates an alkyl hydroperoxide intermediate to the alcohol, ketone, and aldehyde products in an oxygen gas dependent reaction, while aldehyde and ketone products can also be formed from the further oxidation of the alcohols in an oxygen gas independent reaction.Partially presented at the 12th North American Catalysis Society Meeting, Lexington, KY, May 1991, Abstract D 26 and the 8th ISHC meeting in August 2–7, 1992, Amsterdam, The Netherlands, Abstract O–13. For previous biomimetic oxidation papers see ref. [1 ].