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  • Wiley-Blackwell  (261)
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  • 1
    Electronic Resource
    Electronic Resource
    Propylene polymerization through supported metallocene/ MAO catalysts: Kinetic analysis and modellingDedicated to Professor Dr. J. Klein on the occasion of his 60th birthday (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 2393-2402 
    Details
    ISSN: 0887-624X
    Keywords: metallocene, supported ; polypropylene, isotatic ; propylene polymerization, kinetics of, modelling of ; polyolefins, particle growth model for ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several propylene polymerizations are carried out with supported metallocene catalyst, prepared by reaction of silica gel with methylaluminoxane and then with rac-dimethylsi-lanediylbis(indenyl)zirconiumdichloride. The rate-time curves obtained are analyzed to understand the influence of support and triisobutylaluminium on the reaction. As a first attempt to model this system we developed a partially new praticle growth model, based on a shell by shell fragmentation hypothesis (gradual break-up from the outside to the inside of the particle), and a final multigrain structure of the particle. A kinetic scheme including the TIBA interaction with the supported catalyst is also presented. The model prediction and the experimental data are compared for the rate-time curves and polymer properties. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080331412
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  • 2
    Electronic Resource
    Electronic Resource
    Röntgenographische Untersuchungen im System SiO2—V2O5 (1963)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 14 (1963), S. 1034-1036 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Radiographical investigations into the SiO2—V2O5 systemIn connection with research into the inhibiting effect of amorphous SiO2 on oil ash corrosion in gas turbines, the SiO2—V2O3 system was subjected to radiographical investigations. It was found that, at temperatures up to 1200° C, no compounds are formed between the components of this system. Nor was it possible to observe the formation of mixed crystals. However, during heat treatment, vanadium pentoxide has the effect of speeding up the crystallisation of amorphous SiO2 (Aerosil). Depending on the test conditions, one thereby obtains cristobalite or tridymite, or the disordered or polytype-structure forms of these modifications.
    Notes: Im Zusammenhang mit dem Studium der inhibitorischen Wirkung von amorphem SiO2 auf die Ölaschenkorrosion bei Gasturbinen wurden im System SiO2—V2O5 röntgenographische Untersuchungen angestellt. Dabei zeigte sich, daß zwischen den Komponenten dieses Systems bei Temperaturen bis zu 1200° C keine Verbindungsbildung eintritt. Auch die Bildung von Mischkristallen konnte nicht beobachtet werden. Vanadiumpentoxyd übt aber während einer Hitzebehandlung übt aber während einer Hitzebehandlung auf amorphes SiO2 (Aerosil) eine kristallisationsbeschleunigende Wirkung aus. Je nach den Versuchsbedingungen entstehen dabei Cristobalit oder Tridymit bzw. die fehlgeordneten oder strukturpolytypen Formen dieser Modifikationen.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19630141204
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  • 3
    Electronic Resource
    Electronic Resource
    Thermospray high-performance liquid chromatography/mass spectrometric determination of cyclosporins (1992)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 684-689 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The cylic undecapeptides cyclosporin (Csp) A, CspD and dihydro CspC (HCspC) were analyzed by high-performance liquid chromatography/thermospray-mass spectrometry (HPLC/TSP-MS) on line with 1-2 pmol injected on column. Mass spectra were characterized by signals corresponding to the [M + H]+ ion as well as fragment ions derived from he loss of 112 (CspA and CspD) or 44, 114 and 114+44 (HCspC) mass units from the parent ion. The same qualitative profile was observed for negative-ion acquisition where the ions were formed by proton abstraction. The application of the technique to the characterization of CspA and its major hydroxylated and dealkylated metabolites in human blood samples is presented.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290061111
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and properties of hydrophilic polymers. III. Ligand effects of the side chains of polyaziridines on metal complexation in aqueous solution (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 2191-2198 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The metal-complexing properties of five different polyaziridines - poly[1-(2-aminoethyl)aziridine], poly(1-acetylaziridine), poly[1-(2-hydroxyethyl)aziridine], poly[1-(2-hydroxyethyl)aziridine-co-1-acetylaziridine], and poly[1-(2-aminoethyl)aziridine] oxine - were investigated in an aqueous solution with regard to the side-chain effects using membrane filtration. The results are discussed and compared with the stability constants of metalcomplexation of the corresponding functional moieties. Poly[1-(2-aminoethyl)aziridine], a poly(aziridine) with neutral nitrogen donors in the side chains, showed similar complexing properties to those of ammonia. The only exceptions are Fe(III) and Cr(III), which cannot form complexes with ammonia but can be retained in the membrane filtration process due to the formation of Fe(III)-colloidal species and hydroxides. The complexing properties of polyaziridines containing hydroxyl groups in the side chains (i.e., poly[1-(2-hydroxyethyl)aziridine] and poly[1-(2-hydroxyethyl) aziridine-co-1-acetylaziridine] can be explained and described by the formation constants with the corresponding hydroxides. The introduction of a carbonyl moiety in the polyaziridine side chain, e.g., polyacetylaziridine, reduces the complexing ability for metal ions because the carbonyl group cannot form complexes with the metal ions investigated. Poly[1-(2-aminoethyl)aziridine]oxine showed the strongest complexing ability in the series of metal ions due to the strong complexing ligand 8-hydroxy quinoline attached to the polymer backbone. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Investigations of the action of flame retardants in cellulose. II: Investigation of the flame-retardant action of polyphosphonitride in cellulose (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 34 (1987), S. 863-869 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Pure regenerated cellulose fibers and those containing various amounts of phosphorus nitride were pyrolyzed under different conditions in the temperature range of 150-440°C. Easily volatile liquid pyrolysis products, the tar fraction of limited volatility, and the charred residue were determined gravimetrically. The liquid volatiles were analyzed by combined gas chromatography/mass spectrometry for their water content. The tarnfraction and the charred residue were inspected by infrared (IR) spectroscopy. The studies revealed that the phosphorus nitride flame retardant enhances the onset of the pyrolytic decomposition and the release of water at substantially lower temperatures as observed for pure cellulose. The water release favors the carbonization and its extent reduces the formation of levoglucosan as a precursor of easily flammable pyrolysis products. Thus phosphorous nitride must be classified into the water release favoring flame retardants.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070340235
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  • 6
    Electronic Resource
    Electronic Resource
    On the Mechanism of Stereospecific Polymerization - Development of a Universal Model to Demonstrate the Relationship Between Metallocene Structure and Polymer Microstructure (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 585-591 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric catalysis ; metallocenes ; polymerizations ; molecular modeling ; reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the discovery of stereorigid bridged metallocenes, soluble catalysts became available for the stereospecific polymerization of α-olefins. A relatively simple mechanism was used to explain the stereospecificity, primarily in terms of the catalyst symmetry. In this paper we demonstrate that the simple rule of thumb that C2-symmetric catalysts produce isotactic and Cs-symmetric catalysts syndiotactic polypropylene is too narrow. The introduction of one methyl group at the Cp ring in the [{iPr(CpFlu)}ZrCl2]/ MAO system (Flu = fluorenyl, MAO = methylalumoxan) reduces the Cs symmetry to C1, and the resulting catalyst produces hemiisotactic polypropylene. The analogous catalyst with a bulkier tert-butyl group at the Cp ring gives isotactic polypropylene. When the C2 symmetry of [{Me2Si(Ind)2}ZrCl2] (Ind = indenyl) is reduced to C1, a metallocene can be obtained that produces atactic polypropylene. We have broken away from the symmetry-based model and developed a universal model, which accurately describes the experimental microstructures of the polymers by considering the four lowestenergy conformers of the metallocene species coordinating to prochiral propene (Rre, Sre, Ssi, and Rsi) and the positional changes that the polymer chain undergoes during insertion. The relative energy levels of the four diastereomers can be determined by molecular modeling calculations; these energy gradations, in particular the size of the energy gaps, are decisive in determining the stereospecificity. Also, the model permits the stereoerrors to be classified and explained. Through this model the stereosequence of a polymer chain can be calculated and predicted.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030414
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  • 7
    Electronic Resource
    Electronic Resource
    Elementary steps in Ziegler-Natta catalysisPresented at the Polymerization and Polycondensation Processes Symposium, 169th National Meeting of the American Chemical Society, Philadelphia, Pennsylvania, April 6-11, 1975. This paper was not received in time to appear in the proceedings published as Applied Polymer Symposium No. 26. (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 2779-2790 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper is a short review of our recent advances in Ziegler-Natta catalyst system of the type (C5H5)2TiRCl/AlEtn Clm. These are, for instance, the electronic changes after complex formation, the parallel reactions of the alkyl and chain transfer between both the Ti centers of two complexes and the Ti center and an Al center of two complexes; furthermore, the alkyl, chain, and chlorine transfers between these complexes and dimer Al-alkyl, the time which the insertion step of one ethylene requires, and the mathematical calculation of the kinetics of the polyreaction.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1976.070201012
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  • 8
    Electronic Resource
    Electronic Resource
    Investigations on the mechanism of flame retardancy in HET acid containing unsaturated polyester resins (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 27 (1982), S. 1629-1641 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unsaturated polyesters containing varying amounts of HET acid (1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic acid) were synthesized and cured with styrene to give flame-retarding unsaturated polyester resins. The thermal properties were investigated by DTA (differential thermal analysis), TVA (thermal volatization analysis), SATVA (subambient thermal volatilization analysis), and weight loss measurements. The studies revealed that the reverse Diels-Alder reaction of the HET acid units present in the polyester backbone proceeds in the temperature range 300-350°C and yields hexachlorocyclopentadiene. The influence of the HET acid content on the mass distribution of the products of pyrolysis (450°C) was analyzed b means of a gas chromatograph coupled with a mass spectrometer. With increasing HET acid content, the total amount of aromatics evolved from the cured resins is decreased. Concurrently, the relative amount of styrene produced is decreased while the relative amounts of toluene and ethyl benzene are increased. This finding strongly suggests that the hexachlorocyclopentadiene interferes as a chain transfer agent with the unzipping reaction of the polystyrene chains. Further support for this interpretation is derived from the enhanced char formation with increasing HET acid content, as observed by the weight loss measurements.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1982.070270520
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  • 9
    Electronic Resource
    Electronic Resource
    Effectiveness factor calculations for immobilized enzyme catalysts (1973)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 15 (1973), S. 879-888 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The steady state, nonlinear diffusion equations which describe reactions in constrained enzyme solutions are of great interest in many biological and engineering applications. As in other types of nonlinear differential equations, exact analytical solutions do not exist except in some simplified cases. In this paper, a general procedure is presented for solving numerically for the substrate concentration profile and effectiveness factor utilizing the transformation method suggested by Na and Na. Design correlations for enzyme solutions constrained within spherical membranes are included. The use of a unique definition of the Thiele Modulus in these charts permits the clear illustration of the effects of substrate concentration and external mass transfer resistances on the overall effectiveness factor for the catalyst particle.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260150505
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetics of a hollow fiber dehydrogenase reactor (1975)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 17 (1975), S. 1029-1050 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A hollow fiber module was used as a reactor for conversion of ethanol to acetaldehyde in the presence of horse liver alcohol dehydrogenase as catalyst. Mass transport rates for NAD+, the overall acetaldehyde generation rate, catalyst effectiveness factors, and the overall order of the reaction with respect to NAD+ concentration were measured. A coupled-substrate reactor with continuous in situ regeneration of cofactor was also examined. Two substrates of opposite redox state were added simultaneously to the feed stream. NADH and acetaldehyde concentrations were monitored in the effluent stream. The cofactor recycle number, or ratio of moles of product to moles of NADH produced, exceeded 10,000 under certain conditions. While decreasing the NAD+ concentration in the feed stream decreased reactor productivity somewhat, it greatly enhanced the ratio of product formed per mole of NAD+ fed to the reactor. It is suggested that high cofactor costs in dehydrogenase reactors may be overcome with efficient in situ regeneration and secondary recovery and recycling of cofactor from the process stream.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260170707
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