Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The isobutylene polymerizations in the presence of BCl₃ were carried out in dichloromethane ([M]=7 mol/l) at-20°C in the presence and absence of PVC. The products of polymerizations in the absence of PVC are oligoisobutylenes with a narrow molecular weight distribution ; their structure was analyzed by ¹H-NMR spectroscopy. In addition to the signals assigned to known unsaturated terminal structures [ 4.62 and 4.82-CH₂C(CH₃)=CH₂, 5.12-CH=C(CH₃)₂], a new intense signal was found at 5.09 ppm and assigned to the structure-CH=C(CH₃)CH₂CH₃. A mixture of isobutylene homopolymers and PVC grafted with isobutylene (approx. 9.5% wt. isobutylene grafted) is formed in the presence of PVC.     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Hydrogen half-cells in molten salts. A potentiometric investigation of the systems (Pt or Au) H2O/H2, OH− in fused alkali nitrates

The potentiometric behaviour of the hydrogen electrodes (Pt or Au) H₂O-H₂, OH_–has been investigated in molten (Na_0·5, K_0·5)NO₃ at 503 K. In both cases the potential of the indifferent electrode could be expressed by the general equation [H₂O]/[H₂] [OH^–] which is different from the one expected on the basis of a Nernstian behaviour of the theoretical overall system 2H₂O+2e=H₂+2OH^–.The experimental findings are discussed in terms of mechanistic models involving the actual electrode surface and the standard potential for the theoretical (reversible) hydrogen electrode is calculated: =–·0V(versus Ag/Ag⁺ 0·07 M).     

Determination of equilibrium silver sulphate concentration in the system Cu-H2SO4-CuSO4-H2O-Ag2SO4-Ag as a function of composition

The value of the ratio \(\gamma _{{\text{Cu}}^{{\text{2 + }}} } /\gamma _{{\text{Ag}}^{\text{ + }} }^2 \) ( \(\gamma _{{\text{Cu}}^{{\text{2 + }}} } ,\gamma _{{\text{Ag}}^{\text{ + }} } \) -are the mean activity coefficients of copper and silver ions, respectively) was calculated from the measured emf of the cell $${\text{Cu(Hg)|H}}_{\text{2}} {\text{SO}}_{\text{4}} {\text{ (}}c_{\text{x}} {\text{)}} - {\text{CuSO}}_{\text{4}} {\text{ (}}c_{\text{y}} {\text{)|Hg}}_{\text{2}} {\text{SO}}_{\text{4}} {\text{, Hg}}$$ and the solubility of Ag₂SO₄ in H₂SO₄ (c _x) and CuSO₄ (c _y) solutions. The concentration of H₂SO₄ in the solution was varied from 0.5 to 2.1 mol dm^?3 that of CuSO₄ from 0.4 mol dm^?3 to saturation. The results were presented as a function: $$\frac{{\gamma _{{\text{Cu}}^{{\text{2 + }}} } }}{{\gamma _{{\text{Ag}}^{\text{ + }} }^2 }} = a_0 + a_1 c_{\text{x}} + a_2 c_{\text{y}} + a_3 c_{\text{x}}^{\text{2}} + a_4 c_{\text{x}} c_{\text{y}} + a_5 c_{\text{y}}^2 .$$ This function allows the estimation of the equilibrium silver ion concentration \(c_{{\text{Ag}}^{\text{ + }} }^{{\text{eq}}} \) in solutions containing both H₂SO₄ and CuSO₄ in the presence of metallic copper. The function is also very useful for the estimation of the \(c_{{\text{Ag}}^{\text{ + }} }^{{\text{eq}}} \) near a working copper electrode.     

Electrochemical behaviour of a new triiron-substituted polyoxomolybdate

A new complex of the Keggin trilacunary polyoxomolybdate (PMo₉) with Fe³⁺ ions, having the formula (PFe₃Mo₉), has been synthesized and characterized by chemical analysis, FT-IR, Raman, UV-VIS-NIR and EPR spectroscopy, as well as by magnetic susceptibility measurements. Cyclic voltammetry performed at different scan rates, pH and supporting electrolyte composition, was used to investigate the electrochemical behaviour of the PFe₃Mo₉ complex in acidic medium and its electrocatalytic effect on H₂O₂ reduction. The voltammetric waves were assigned, and the enhanced electrocatalytic efficiency of PFe₃Mo₉ relative to PMo₉ was attributed to the presence of Fe atoms.     

Analysis of the kinetics for the H2 + - \frac{1}{2}O2 ⇌ H2O reaction on a hot Pt surface in the pressure range 0.10–10 Torr

The H₂ + O₂ ⇌ H₂O reaction on platinum at 700 and 1300 K has been studied. A stagnation flow geometry was used with a gas mixture of H₂ and O₂ at pressures between 0.10 and 10 Torr. Comparing SHG results with simulations using different reaction parameters, it was concluded that , and . LIF measurements showed an ambiguity in the choice of main water-producing channel. Both hydrogen addition with low sticking coefficients and hydroxyl disproportionation with high sticking coefficients are plausible. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of total monomer concentration on the “reactivity” of ω-(p-vinylbenzyl ether) macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) determined from radiacal copolymerization experiments with butyl methacrylate

Summary The influence of the total monomer concentration on the radical reactivity ratio r₁ of butyl methacrylate (BMA) (M₁)--(p-vinylbenzyl ether) macromonomer of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-VBE) (M₂) monomer pair was investigated. For two different molecular weights of the PPO-VBE macromonomer ( , and ), the determined reactivity ratio r₁ decreases with the increase of the macromonomer concentration. Therefore, the reactivity of the macromonomer, 1/r₁, follows the opposite trend. This dependence is due to micelles formation during copolymerization. This microsegregation process partitionates the comonomer concentrations between the bulk of solvent and around the growing chain and therefore, the experimental r₁ is actually a product of the true reactivity ratio r₁ ⁰ and a partition coefficient k.     

Polymerization of substituted acetylenes by (mesitylene)M(CO)3 (M=W,Mo)

Summary Phenylacetylene could be polymerized by (mesitylene)W(CO)₃ in CCl₄ to give a polymer with 12,000 in ca. 80% yield. UV irradiation was unnecessary unlike the W(CO)₆–CCl₄-h catalyst. The present polymerization did not proceed in toluene. The (mesitylene)W(CO)₃ catalyst afforded high molecular weight polymers from phenylacetylenes bearing bulky substituents (e.g., Me₃Si and CF₃) at the ortho position. The Mo counterpart, (mesitylene)Mo(CO)₃, catalyzed the polymerization of 1-chloro-2-phenylacetylene and 1-chloro-1-octyne to provide high molecular weight polymers . Catalytic amounts of Lewis acids accelerated the polymerization of phenylacetylene by (mesitylene)W(CO)₃, but decreased the polymer molecular weight; this polymerization proceeded not only in CCl₄ but also in toluene.     

[CuL(H2O)2]{[CuL][Fe(CN)6]}2·2H2O (L=3,10-Bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane): A Novel Three-Dimensional Coordination Polymer via H-Bonded Linkages of One-Dimensional Zigzag Chain

A complex with the formula [CuL(H₂O)₂]{[CuL][Fe(CN)₆]}₂·2H₂O, where L=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane, has been synthesized and crystallographically characterized. The structure is composed of a one-dimensional zigzag chain of units, and [CuL(H₂O)₂]²⁺ units. The one-dimensional zigzag chain extents through linkages. The adjacent two polymer chains are linked by the hydrogen bonding between [CuL(H₂O)₂]²⁺ and [Fe(CN)₆]^3–, forming a 3D supramolecular structure with inner hydrophilic channels. Magnetic susceptibility measurements show no exchange interaction between the Cu(II) and Fe(III) ions due to the longer (axial) bond length.     

Influence of temperature on the electro-dissolution of tin in NaCl aqueous solution at pH4

The influence of temperature in the range 25 to 80°C on the dissolution of tin was investigated in an acidic solution at pH4 containing 0.1 to 1m NaCl. The corrosion current is slightly dependent on both the temperature and the Cl^– ion concentration. The main dissolution characteristics of tin are

Measurement and regulation of oxygen content in selected gases using solid electrolyte cells. IV. Accurate preparation of CO2-CO and H2O-H2 mixtures

Mixtures of CO₂-CO, H₂O-H₂ and Ar-H₂O-H₂ of precise composition were prepared using a zirconia pump and analysed with a zirconia gauge. The ratio was varied from 5×10^–2 to 10⁴ and the ratio from 3×10^–4 to 10^–2. A Faraday's Law test proved to be a simple and reliable procedure for checking the conditions of utilization of these gaseous mixtures and for verifying that no significant disproportionation of CO or leakage along the gas circuit altered the prepared composition. From a practical point of view the best methods of preparing mixtures with low oxygen activity are reduction of carbon dioxide in the range 5×10^–11 to 10^–17 atm and oxidation of inert gas-H₂ in the range 10^–19 to 10^–27 atm at 800°C.     

Study of macroinitiator efficiency and microstructure–thermal properties in the atom transfer radical polymerization of methyl methacrylate

The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with poly vinylacetate macroinitiator (PVAc-CCl₃) and CuCl/PMDETA as catalyst was successfully carried out in bulk and solution. The apparent propagation rate constant () and concentration of active species ([P°]) were higher in the bulk. In solution they increased with polarity of solvent. Two different molecular weights of macroinitiators were used in ATRP of MMA. The linear relation of Ln[M]₀/[M] versus time was only confirmed for the low molecular weight macroinitiator. The ratio of was calculated in the bulk reaction with the low molecular weight macroinitiator, this ratio was 1.77 × 10¹⁴ M⁻¹ s⁻¹ for larger macroinitiator in solution. The MWD of block copolymers were sharper with lower molecular weight macroinitiator in the solution, but it appeared broader in the bulk polymerization. Our results indicated that smaller molecular weight macroinitiator was more efficient and formed a block copolymer with lower PDI. Thermal analysis and microstructure of the block copolymers are investigated by ¹H NMR, FT-IR, TGA and DSC. The chain tacticity of the MMA units is found not to be sensitive to the kinetic of the reactions with two different molecular weights of macroinitiator. DSC measurement shows two different transitions at 39 and 108 °C assigned to PVAc and PMMA blocks. The TGA profile shows a three-step degradation. The initial small weight loss that occurs around 220 °C and two large weight loss around 238 and 310 °C are attributed to dechlorination step and decomposition of the PMMA and PVAc blocks.     

Synthesis and characterization of polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide)

Summary Free radical copolymerization of acrylonitrile (AN, M₁) with poly(2,6-dimethyl-1,4-phenylene oxide)--vinylbenzyl ether (PPO-VBE, M₂, _n + 4200g/mol, _w/ _n + 1.04) was performed at 60°C in either a mixture of N,N-dimethylformamide/toluene or tetrahydrofuran, using 2,2-azoisobutyronitrile (AIBN) as initiator. The characterization of the resulting polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide) (PAN-g-PPO) was performed by 200 MHz ¹H-NMR spectroscopy and solubility.     

Enhanced mass transfer in electrochemical cells using turbulence promoters

Many electrochemical processes suffer in varying degrees from mass transfer limitations. These limitations may require operation at considerably less than economic optimum current densities. Mass transfer to a surface may be considerably enhanced by insertion of turbulence promoters in the fluid flow path near the affected surface.An instrument was developed to measure local current densities in the hydrodynamically very difficult region near the turbulence promoter. A general method for the relative evaluation of hydrodynamic conditions has been developed. Generalization of the data permits optimization of hydrodynamic cell design using the promoter shapes investigated.

Notation

Symbols A Coefficient for cell power costs, $ m² (As)^–1 - A _c Cell area, m² - a Constant in Equation 4 - B Coefficient for area-proportional costs, $ A (m² s)^–1 - C Coefficient for pumping power costs, $ A (m² s)^–1 - C _b Bulk concentration, kg mol m^–3 - C _bi Inlet bulk concentration, kg mol m^–3 - C _e Energy cost, $ (Ws)^–1 - C _i Interfacial concentration, kg mol m^–3 - ¯C _s Amortized area cost, $ (m² s)^–1 - D Current—density-insensitive costs, $ s^–1 - D _e Equivalent diameter, m - D Diffusion constant, m² s^–1 - e Current efficiency - F _d Cell feed rate, m³ s^–1 - F 96.5×10⁶ A s kg eq^–1 - g Channel width, m - h Channel height, m - i Current density, A m^–2 - i _opt Economic optimum current density, A m^–2 - K Total costs of running cell, $ s^–1 - (K–D)_ideal Total sensitive costs under hydrodynamically ideal conditions, $ s^–1 - k _c Convective mass transfer coefficient, m s^–1 - L Total length of flow path, m - l Promoter spacing, m - N Mass flow rate to surface due to convection, kg mol m² s^–1 - n _e Number of electrons transferred in electrode reaction - P _c Power required by cell, W - P/L Average pressure gradient in channel, N m^–3 - R _av Effective cell resistance, m² - S Open channel cross-section, m² - S ₀ Minimum channel cross-section at promoter, m² - s _i Stoichiometric coefficient of species i - t _i Transport number of species i in solution - ¯t _i Effective tranport number of species at polarized surface - V Average fluid velocity, m s^–1 - x Distance from inception of concentration disturbance, m - ₁ Electrical power conversion efficiency - ₂ Pumping power conversion efficiency - Solution viscosity, kg (m s)^–1 - Solution density, kg m^–3 Dimemionless groups Fanning friction factor - Reynolds number - R h/g Channel aspect ratio - D _e/l Promoter frequency - S/S ₀ Contraction coefficient - Sherwood number - Degree of reaction - Dimensionless total sensitive - Dimensionless current density - Energy cost ratio     

Raman study of chain deformation in polypropylene

Summary Raman spectroscopy was used to study the transfer of energy that occurs among the internal vibrations of crystalline isotactic polypropylene as it is compressed. The group was found to play a significant role in the subsequent chain deformation.     

The film model for determining the effect of ionic migration in electrochemical systems

The film model is used to examine the effect of ionic migration on the concentration of ionic species and on the electrolyte potential profiles inside the Nernst layer.A general analytical solution is obtained which allows the variation of the limiting current density with the total concentration of the species present in the electrolyte to be demonstrated. Two cases are considered depending on whether the product is soluble in the electrolyte or not. Specific examples are given for the reduction of cupric ions (cations) or ferricyanide ions (anions), respectively in H₂SO₄ and KOH electrolyte.Nomenclature C _j concentration of ionic species inside the diffusion layer - C _jo concentration of ionic species in the bulk - C _A,C _B concentration of the reactant and product inside the diffusion layer - D _j molecular diffusion coefficient - F Faraday's constant - i current density - n exponent ofD _j - i _L,i _L0 limiting current densities - r ratio - T temperature - r c _B0/c _A0 - t _j transport number - x normal coordinate - y as defined in Equation 36 - Z _j charge number of speciesj - z _AB mutual charge number defined in Equation 11 - z number of electrons involved in the reaction Greek letters diffusion layer thickness - electrical solution potential     

Fundamental studies on a new concept of flue gas desulphurization

A new process for removal of sulphur dioxide from waste gases is proposed consisting of both electrochemical and catalytic sulphur dioxide oxidation. In the catalytic step a part of the sulphur dioxide is oxidized by oxygen on copper producing sulphuric acid and copper sulphate. The other part is oxidized electrochemically on graphite. The cathodic reaction of this electrolysis is used for recovering the copper dissolved in the catalytic step. The basic reactions of this process have been studied experimentally in detail. It has been shown that sulphur dioxide can be electrochemically oxidized on carbon electrodes to sulphuric acid with high current efficiency. The reaction rate of the electrochemical copper deposition is increased by dissolved sulphur dioxide in the electrolyte. The catalytic oxidation of sulphur dioxide on copper has been investigated for different sulphur dioxide concentrations and temperatures. The ratio of the reaction products, sulphuric acid and copper sulphate, varies over a wide range depending on the experimental conditions.Nomenclature SO₂ concentration (gas phase) (vol % SO₂) - SO₂ concentration (electrolyte) (g l^–1) - E potential vs saturated calomel electrode (V) - E _s specific energy consumption (W g^–1 SO₂) - F Faraday constant (A s^–1 mol^–1) - i current density (mA cm^–2) - molecular weight (g mol^–1) - T temperature (° C) - U _c cell voltage (V) - v _e number of electrons being transferred - space-time yield of SO₂-oxidation (g SO₂ h^–1 dm^–3) - _cu space-time yield of Cu-corrosion (g Cu h^–1 dm^–3) - ratio - fractional conversion of SO₂ - current efficiency for SO₂ oxidation     

Study of mass transfer in a vertically moving particle bed electrode

A study was made of the influence of process parameters on the mass-transfer coefficient in a flow-through cell with a cascade of rotating drums partially filled with conductive particles (called the vertically moving particle bed). Copper deposition from an acidic sodium sulphate solution was used as the model reaction. To evaluate the experimental data a macrohomogeneous mathematical model of potential and current density distribution inside the cell was developed. The electrolyte flow distribution between the empty space above the particle bed and through the bed was evaluated. On the basis of these results the following correlation is proposed:

Solid state ionics—the electrochemical analog memory cell with solid electrolyte

A new type analog memory cell with variable output voltage has been proposed and its performance examined. The cell construction is $$\begin{gathered} {\text{Ag|RbAg}}_{\text{4}} {\text{I}}_{\text{5}} {\text{|(Ag}}_{\text{2}} {\text{Se)}}_{{\text{0}} \cdot {\text{925}}} {\text{(Ag}}_{\text{3}} {\text{PO}}_{\text{4}} {\text{)}}_{{\text{0}} \cdot {\text{075}}} {\text{|RbAg}}_{\text{4}} {\text{I}}_{\text{5}} {\text{|Ag}} \hfill \\ {\text{ }} \uparrow \hfill \\ {\text{ Pt}} \hfill \\ \end{gathered} $$ in which (Ag₂Se)_0.925(Ag₃PO₄)_0.075 is a mixed conductor exhibiting high ionic and electronic conductivity at room temperature. The potential difference between the silver electrode and the platinum electrode depends on the silver activity in the mixed conductor, and it is changed by passing the current between one silver electrode and the platinum electrode. The output voltage of the cell is changed in the range of 150 to 0 mV. At open circuit, the memorized cell voltage decreased by only 1% over several hours.     

Facile Electrospinning Preparation and Up-Conversion Luminescence Performance of Y3Al5O12:Er3+, Yb3+ Nanobelts

Electrospinning technique was used to prepare $ {\text{PVP}}/\left[ {{\text{Y}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Yb}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Er}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Al}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} } \right] $ composite nanobelts and novel structures of Y₃Al₅O₁₂:Er³⁺, Yb³⁺ (denoted as YAG:Er³⁺, Yb³⁺ for short) nanobelts have been successfully fabricated after calcination of the relevant composite nanobelts at 900 °C for 8 h. YAG:Er³⁺, Yb³⁺ nanobelts were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy. XRD analysis indicated that YAG:Er³⁺, Yb³⁺ nanobelts were cubic in structure with space group I_a3d. SEM analysis and histograms revealed that the width of YAG:Er³⁺, Yb³⁺ nanobelts was ca. 1.8 ± 0.37 μm under the 95 % confidence level, and the thickness was ca. 81.8 nm. Up-conversion emission spectra analysis manifested that YAG:Er³⁺, Yb³⁺ nanobelts respectively emitted strong green and red emissions centering at 522, 554 and 648 nm under the excitation of a 980-nm diode laser. The green emissions were assigned to the energy levels transitions of $ ^{ 2} {\text{H}}_{ 1 1/ 2} ,^{ 4} {\text{S}}_{ 3/ 2} \to^{ 4} {\text{I}}_{ 1 5/ 2} $ of Er³⁺ ions, and the red emission originated from the energy levels transition of $ ^{ 4} {\text{F}}_{ 9/ 2} \to ^{ 4} {\text{I}}_{{{\text{l5}}/ 2}} $ of Er³⁺ ions. The up-conversion luminescence of YAG:Er³⁺, Yb³⁺ nanobelts doped with various concentrations of Yb³⁺ and Er³⁺ was studied and the optimum molar ratio of Yb³⁺ to Er³⁺ was found to be 15:1. CIE analysis demonstrated that color-tuned luminescence can be obtained by adjusting doping concentrations of Yb³⁺ and Er³⁺ ions, which could be applied in the fields of optical telecommunication and optoelectronic devices. The up-conversion luminescent mechanism and the formation mechanism of YAG:Er³⁺, Yb³⁺ nanobelts were also proposed.