Polymerization mechanism of vinyl chloride with titanium tetrabutoxide–ethylaluminum sesquichloride catalyst and some physical properties of poly(vinyl chloride) prepared at low temperature

The mechanism of vinyl chloride polymerization by titanium tetrabutoxide–ethylaluminum sesquichloride catalyst system was investigated from the view of the stereoregularity of poly(vinyl chloride). The samples were prepared at a selected temperature in the range from 23 to ?78°C. The tactic triads, obtained from 220-MHz NMR spectra, show clearly the adequacy of Bernoullian statistics in describing the mechanism for stereochemical propagation. The chain propagation proceeds according to Bernoullian statistics with syndiotactic placements favored by 550 cal/mole. These results suggest that vinyl chloride polymerizes by a free-radical mechanism under the action of the present catalyst system.     

Nature of the active component in the catalytic system prepared from titanium(III) chloride(AA), ethylaluminum dichloride,and tetrakis(dimethylamino)silane,in the polymerization of propylene

The chemistry of the titanium(III) chloride(AA)–ethylaluminum dichloride–tetrakis-(dimethylamino)silane system for the polymerization of propylene was studied. A complex of ethylaluminum dichloride with tetrakis(dimethylamino)silane was isolated. It was shown that this complex contains ethylaluminum dichloride and tetrakis(dimethylamino)silane in the ratio of 2:1. This complex with titanium(III) chloride is responsible for the polymerization activity.     

Polymerization of ethylene catalyzed by diethylaluminum chloride and titanium (III) acetylacetonate

Catalysts for the polymerization of ethylene were prepared from titanium (III) acetylacetonate and diethylaluminum chloride. Titanium (III) acetylacetonate is of interest because it is soluble in hydrocarbon solvents used as polymerization media. As its oxidation product oxobisacetylacetonatotitanium (IV) is also hydrocarbon-soluble, this system provides a vehicle for studying the effects of a change in valence on catalyst activity without an accompanying change of state, as occurs with titanium halides. Relatively high molar ratios (>20:1) of aluminum alkyl to titanium compound were required to give active catalysts. Precipitates generally formed in the catalyst mixtures, although dilute catalyst solutions in which no precipitate was visible still initiated polymerization. Catalyst mixtures were observed to undergo certain changes on standing. Light-scattering studies indicated an increase in catalyst particle size, and a gas identified as ethane was evolved. These changes were accompanied by a reduction in activity of the catalyst. Parallel polymerization tests were run for a comparison of catalysts prepared from titanium(III) acetylacetonate and catalysts prepared from oxobisacetylacetonatotitanium(IV). There was essentially no difference in yield or properties of polymer prepared using the two catalyst systems. The evidence suggests that both the trivalent and tetravalent titanium compounds yield the same catalytic intermediate when reacting with diethylaluminum chloride.     

Effect of europium(III) chloride on the aggregation behavior of sodium dodecyl sulfate

The effect of EuCl3 on the aggregation processes of sodium dodecyl sulfate was investigated. Electrical conductivity data, combined with Eu(III) luminescence measurements, suggest that the formation of micelles involving EuCl3 and SDS occurs at low SDS concentration; the formation of these mixed aggregates was also monitored by light scattering, which indicates that the addition of EuCl3 to SDS concentration at values below the critical micelle concentration of the pure surfactant results in a much higher light scattering than that found just with SDS micelles. It was also found that the Eu(III)/DS- complexes are formed with a binding ratio which varies between 20 and 4, depending on the initial concentration of Eu(III). As the concentration increases, turbidity occurs initially, but solutions become clear subsequently. In contrast to the behavior of SDS in the presence of aluminum(III), no flocculation was observed. From the analysis of electrical conductivity data and comparison with other systems, it is suggested that growth of aggregates happens, probably with formation of nonspherical systems. At the highest concentrations these may involve just Eu(III) and DS- ions. The effect of temperature on the SDS micellization process was studied. The calculated free energy of SDS micellization is not dependent on the initial EuCl3 but is dependent on the final balance between the presence of counterions in solution (ionic strength) and the temperature.     

Polymerization of vinyl chloride and copolymerization with propylene by a ternary catalyst system

Polymerization of vinyl chloride by the ternary catalyst system of VOCl₃–AIR_nCl_3–n complexing agent was investigated. It was suggested that the formation of a polar complex (or charge-transfer complex) between AlR_nCl_3–n and the complexing agent participated in the polymerization of vinyl chloride. In the copolymerization of vinyl chloride with propylene with the present catalyst system, it was more difficult to incorporate the propylene unit in the copolymer than with a typical radical catalyst.     

Polymerization of acrylamide and methacrylamide photoinitiated by azidopentamminecobalt(III) chloride

The kinetics of polymerization of acrylamide and methacrylamide, photoinitiated by azidopentamminecobalt(III) chloride in homogeneous aqueous acid medium was studied systematically. Monochromatic wavelengths 365, 405, and 435 mμ were employed for irradiation. Polymerization proceeded without any induction period, and the reaction was followed by measurements of rate of monomer disappearance (bromometrically), rate of complex disappearance (spectrophotometrically), and the chain lengths of the polymer formed (viscometrically). The dependences of the rate of polymerization on variables like light intensity, light absorption fraction by the complex, wavelength, monomer concentration, hydrogen ion concentration, nature of the acid used (HClO₄, HNO₃, and H₂SO₄), etc., were studied. The rate of polymerization of acrylamide depended on the unit power of monomer concentration and on the square root of light absorption fraction k_ε and light intensity I. The rate of methacrylamide polymerization was proportional to the unit power of monomer concentration and fractional powers of 0.25 and 0.30 of k_ε and I, respectively. A kinetic reaction scheme is proposed and discussed in the light of the experimental results, and it has been concluded that (1) the primary photochemical act is an electron transfer reaction from the azide ion to Co(III) in the complex, (2) initiation of polymerization is by azide radical, (3) termination is by mutual destruction of polymer radicals.     

Cyclotrimerization of acetylene by the tris(acetylacetonato)titanium(III)–diethylaluminum chloride system

Reaction of acetylene with tris(acetylacetonato)titanium(III) and diethylaluminum chloride system leads to formation of benzene, a trace of ethylbenzene, and a small amount of polyacetylene. The isotopic composition of products obtained from cyclotrimerization of acetylene-d₂ and an equimolar mixture of acetylene and acetylene-d₂ is investigated to elucidate the mechanism of the cyclotrimerization. The results suggest a mechanism in which an acetylene inserts into the metal—ethyl bond formed by reaction of Ti(acac)₃ and Al(C₂H₅)₂Cl, followed by insertion of two acetylene molecules and elimination of a hydrogen atom from the first inserted acetylene to yield an ethylbenzene and a metal hydride intermediate. The metal hydride intermediate catalyzes acetylene cyclotrimerization to give benzene. During the reaction, the hydrogen atom in the metal hydride intermediate does not exchange with the hydrogen atom in the inserted acetylene molecules.     

Mild and efficient allylation of aldehydes mediated by titanium(III) chloride

A mild, chemoselective and efficient method for the allylation of aldehydes is described. Ketones remained unreacted under the reaction conditions.     

Thermodynamics of aqueous mixtures of sodium chloride,potassium chloride,sodium sulfate,and potassium sulfate at 25°C

Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate can be mixed in six ways to give ternary mixtures. Two of these have already been studied and results are now presented for the remaining four systems: H₂O–NaCl–K₂SO₄, H₂O–Na₂SO₄–K₂SO₄, H₂O–KCl–Na₂SO₄, and H₂O–KCl–K₂SO₄.     

Polymerization of β-cyanopropionaldehyde. III. Polymerization by organoaluminum and by organoaluminum–titanium chloride complexes

The mechanism of formation and stereoregularity of poly(cyanoethyl)oxymethylene have been studied. The polymerization was carried out at ?78°C with use of aluminum compounds [Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(C₂H₅)Cl₂, and AlCl₃] and complex catalysts [Al(C₂H₅)₃–TiCl₄, Al(C₂H₅)₃–TiCl₃, and Al(C₂H₅)₂Cl–TiCl₃] as initiators. The stereoregularity of poly(cyanoethyl)oxymethylene was estimated from the optical density ratio, D₁₂₅₈/D₁₂₇₀, in the infrared absorption spectrum. Polymer yields were observed to depend upon the aluminum compound used as initiators, while the stereoregularity of the polymer was nearly independent of the particular aluminum compound used. As the catalyst ratio of titanium chloride to aluminum compound increased, the polymer yield was found to increase to a maximum and then to decrease with further increase of the ratio. It is supposed that titanium chlorides themselves increase the acid strength of aluminum compounds through chlorination, resulting in the change of the polymer yield. The highest stereoregularity of poly(cyanoethyl)oxymethylene was attained by increasing the molar ratio of titanium trichloride to aluminum and by treating β-cyanopropionaldehyde (CPA) with titanium trichloride prior to the polymerization. Complex formation of the nitrile group of CPA with titanium is considered responsible for the increase in stereoregularity. A propagation mechanism is also proposed.     

Precipitation of monodispersed basic iron(III) sulfate (sodium jarosite) particles

Uniform sodium jarosite particles were obtained by forced hydrolysis of ferric salt solutions to which copper sulfate, sodium sulfate, and sodium nitrate were added. It was found that at the same concentrations of ferric and sulfate ions the particle size and yield decreased with the lowering of the concentration of sodium ions, but the morphology remained the same. At a sufficiently small content of sodium in the reacting solution, no precipitation of sodium jarosite particles was observed. Finally, chemical and XRD analyses showed that small amounts of copper ions are incorporated in the crystal lattice which, with the change in the Na⁺/H₃O⁺ ratio, slightly affected the structure of this mineral, but not its other properties. Received: 12 July 2000 Accepted: 18 August 2000     

Studies and microdetermination of some organic sulfur functions by reduction with titanium(III) sulfate solution

Micromethods are described for the determination of organic sulfoxides and disulfides based on reduction with titanium (III) sulfate solution, the excess of which is titrated with standard ferric alum as usual. The procedures developed depended on the nature of the compound whether aromatic or aliphatic. Quantitative reduction of sulfoxides was achieved in presence of ammonium thiocyanate and sodium acetate but whereas aryl sulfoxides required heating at 70 °C for 30 minutes, the alkyl members demanded heating at 90 °C for one hour. Complete reduction of disulfides was possible in presence of acetate buffer and heating at 50 °C for 15 minutes for aromatic disulfides and at 80 °C for 30 minutes in case of the aliphatic ones. a Calculated by dividing the total titer in a ratio of 2:12. b Calculated using the total titer consumed. Sulfonyl halides, thiocyanates, and isothiocyanates do not react with the titanium(III) solution. The effect of the various sulfur functions on the determination of the nitro group with titanium(III) was also studied and various nitro-substituted sulfur compounds were successfully analyzed.     

Molybdenum and copper catalysis of reductions by titanium(II) and titanium(III)

Reductions of vanadium(IV), benzoquinone, and tri-iodide, both by titanium(III) and by titanium(II), are catalyzed by molybdenum(VI). The VO(2+)-Ti(II) reaction is catalyzed by copper(II) as well. Reactions of Ti(II) with the oxidant in excess yield Ti(IV), as do reductions by Ti(III). Reactions proceed via competing uncatalyzed and catalyzed paths, with the latter components first order in catalyst. Kinetic patterns indicate that monomeric Mo(v) is the active species, but the dimeric Mo(v) species, [Mo(2)O(4)](2+), is without catalytic action. Catalytic constants pertaining to Ti(III) are remarkably similar to those for Ti(II), despite the 0.47 V difference in the standard potentials of the two reductants.     

Reduction of ammonium nitrate with titanium(III) chloride in acid media

Investigation of acid ammonium nitrate solutions in the presence of titanous chloride has led to a new mechanism of nitrate reduction. It is proposed that the reduction proceeds through two electron changes and terminates as nitrous oxide in solutions whose acid content is greater than 0.1 N. The stronger reducing power of the titanous buffer method previously reported arising from a direct pH affect on the titanous -titanyl couple has been discerned rather as an effect arising from different reduction products in that media. The affects of prolonged reaction at 100° and use of osmium tetroxide catalyst were examined. A pH of 4.5 and 100% excess of titanous was insufficient to reduce nitrate to ammonia quantitatively.     

Polymerization of acrylonitrile initiated by a manganese(III) acetate glycerol redox system

The kinetics of polymerization of acrylonitrile(AN) initiated by manganese(III) acetate in the presence of glycerol was investigated in the temperature range of 30–40°C. The effect of varying the concentrations of glycerol, sulfuric acid, acetic acid, metal ion, and monomer on the rate was studied. A suitable reaction scheme and rate expression have been proposed. Termination was mutual and was caused by the combination of two growing polymer radicals.     

Efflorescence relative humidity of mixed sodium chloride and sodium sulfate particles

We study the efflorescence relative humidity (ERH) of particles composed of sodium chloride and sodium sulfate. Both experimental and theoretical investigations are conducted to explore the effects of particle size and mixing ratios between two inorganic materials on ERH. A previously developed theoretical model (Gao et al. J. Phys. Chem. A 2006, 110, 7602; ref 1) is applied as the framework to build a formulation assuming that one salt nucleates much faster than the other, and the critical nuclei formation of the former controls the rate of efflorescence. The predicted ERHs agree favorably with the experimental data, except for particles containing Na2SO4 in a mole fraction of around 0.25. At this composition, our model underestimates the ERH, indicating certain factors involved in the efflorescent processes that are overlooked in our formulation. Relative to particles larger than 40 nm, the Kelvin effect more significantly affects particles smaller than this size.     

Spectrophotometric flow-injection determination of nitrate based on reduction with titanium(III) chloride

Nitrate (0.02– μg N ml^?1) is determined by injection into a water carrier which merges with a 6% (w/v) titanium(III) chloride stream. The nitrale formed is reacted with sulphanilamide and N-(1-naphthyl)ethylenediamine, and the resulting azo compound is quantified spectrophotometrically at 530 nm. Of the common ions, only copper(II) interferes; it is removed by an on-line cation-exchange minicolumn. The method is applied to potable waters.     

Micellar effect of sodium dodecyl sulfate on the reactions between iron(II) and p-benzoquinone, and iron(III) and hydroquinone

The micellar effet of sodium dodecyl sulfate (SDS) on the initial stages of the reaction between (1) Fe(II) and p-benzoquinone, and (2) Fe(III) and hydroquinone have been investigated. In the former case acceleration was observed, the rate-[surfactant] profile showing a maximum. SDS has an inhibitory effect on the latter reaction. Kinetic analysis has been carried out using Berezin's approach.

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() 1) Fe(II) 2) Fe(III) . - . . , .