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  • Chemistry  (23)
  • Lunar and Planetary Science and Exploration
  • 1995-1999  (22)
  • 1925-1929  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Stereoselective polymerization of butadiene by a new dicationic nickel complex (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 239 (1996), S. 33-41 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der neuartige dikationische Komplex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-Bis(diphenylphosphin)ferrocen) zeigte in Anwesenheit von Diethylaluminiumchlorid (AIEt2CI) hohe Aktivität für die Polymerisation von 1,3-Butadien. Reaktionsdauer, Temperatur und das Aluminium/Nickel-Verhältnis wurden auf maximale Aktivität und Selektivität optimiert. Umsätze über 90% konnten erreicht werden. Im Vergleich zu Polybutadienen, die mit anderen Nickel-Phosphin-Systemen hergestellt wurden, zeigten die synthetisierten Polybutadiene höhere cis-1,4-Anteile (〈80%) und eine geringe Bildung von 1,2-Einheiten (2%). Alle Polymeren hatten niedrige mittlere Molekulargewichte (Mw 〉 11 800).
    Notes: The new dicationic nickel complex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene) in the presence of diethylaluminium chloride (AIEt2CI) exhibited high activity on the 1,3-butadiene polymerization. Reaction time, temperature and aluminium/nickel molar ratio were optimized in order to achieve maximum activity and selectivity. Conversions higher than 90% were obtained in contrast to other nickel-based systems using phosphine ligands, the resulting polybutadiene showed high cis-1,4 (〈80%) content and only small amount of 1,2-units (2%). All polymers presented low molecular weights (Mw 〉 11 800).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1996.052390104
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  • 2
    Electronic Resource
    Electronic Resource
    Complexity of the hydrolytic degradation of aliphatic polyesters (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 239-253 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aliphatic polyesters are more or less hydrolytically degradable, depending on their chemical, configurational and morphological structures. Hydrolysis can be either homogeneous or heterogeneous, depending on many structural and environmental factors. The present understanding of this hydrolytic degradation is recalled. The importance of diffusion-reaction phenomena is discussed on the basis of the behaviors of polyesters derived from α-hydroxy acids, namely lactic and glycolic acids and attempts are made to extend the understanding to other members of the aliphatic polyester family. The main results of some recent investigations of the effects on poly(lactic acid) polymers of basic additives and of initiators such as stannous octoate and zinc metal, which are now industrially used, are presented.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052470116
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  • 3
    Electronic Resource
    Electronic Resource
    Kupfer(II)-chlorid-katalysierte ‘Carben-Dimerisierung’ von 1-Halogeno-1-Lithiocyclopropanen: Ein einfacher Zugang zu Bi(cyclopropylidenen)Herrn Prof. Dr. Richard Neidlein zum 65. Geburtstag gewidmet14. Mitt. über Kupplungsreaktionen, 13. Mitt.: [1] (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1144-1165 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II)-Chloride Catalyzed ‘Carbene Dimerization’ of 1-Halogeno-1-lithiocyclopropanes: A Simple Access to Bi(cyclopropylidenes)A series of 13 bi(cyclopropylidenes) 11 are prepared in a simple one-pot reaction by halogeno-lithio exchange between 1,1-dibromocyclopropanes 1a-n and BuLi, in most cases at -95°, to give 1-bromo-1-lithiocyclopropanes 2a-n, followed by treatment with CuCl2 at low temperature and a simple workup at room temperature (Scheme 3c and Table 1). The yields of bi(cyclopropylidenes) 11 strongly depend on reaction parameters, as explicitly shown for the conversion 1f →→ 11f (Tables 2-8). Mixed couplings between two different carbenoids are possible (Scheme 4), while diastereoselectivity of the active transition-metal complex seems to be low. The structures of bi(cyclopropylidenes) 11 are confirmed by spectroscopic data as well as by X-ray analysis of an isolated crystalline diastereoisomer of 11k (Fig. 1).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780509
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  • 4
    Electronic Resource
    Electronic Resource
    Die Reaktion von 1-Halogeno-1-Lithiocyclopropanen mit CuCl2: Konkurrenz zwischen ‘Carben-Dimerisierung’ und oxidativer Kupplung15. Mitt. über Kupplungsreaktionen, 14. Mitt. [1]. (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1311-1324 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Reaction of 1-Halogeno-1-lithiocyclopropanes with CuCl2: Competition between ‘Carbene Dimerization’ and Oxidative CouplingThe 1-chloro-1-lithiocyclopropanes 2a-d react at low temperature with CuCl2 to give diastereoisomeric mixtures of oxidative-coupling products 5a-d and of ‘carbene dimers’ 6a-d. The relative amount of 5a-d increases with CuCl2 concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1′-dichloro-1,1′-bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a-d, 1-bromo-1-lithiocyclopropanes normally react with CuCl2 to give ‘carbene dimers’ 6 and no coupling products 5. So far the only exception is 1-bromo-1-lithio-2-phenylcyclopropane 2e which in the presence of CuCl2 gives some percents of coupling products 5e besides carbene dimers 6b as main products. An X-ray structure analysis of the predominant diastereoisomer 5e was performed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780521
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  • 5
    Electronic Resource
    Electronic Resource
    More about the polymerization of lactides in the presence of stannous octoate (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3431-3440 
    Details
    ISSN: 0887-624X
    Keywords: lactide ; polylactide ; polymerization ; mechanism ; stannous octoate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring-opening polymerization of lactide cyclic monomers in the bulk in the presence of tin(II) 2-ethylhexanoate (stannous octoate or SnOct2) was reexamined under conditions allowing for the end group characterization of growing chains by high-resolution 1H-NMR. Data collected for low values of the monomer/initiator (M/I) ratio showed that the DL-lactide ring was opened to yield lactyl octoate-terminated short chains. A cationic-type mechanism involving co-initiation by octanoic acid was proposed to account for experimental findings. The formation of a side product, hydroxytin(II) lactate (HTL), was found which appeared able to initiate lactide polymerization and to yield a high molecular weight PLA50 polymer. However the polymerization with stannous octoate was faster than the HTL one. Anyhow, data suggested that both SnOct2 and HTL are likely to act simultaneously as initiators during the polymerization of lactides in the presence of SnOct2. A complete reaction scheme was proposed to account for the presence of the various compounds likely to be formed under these conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3431-3440, 1997
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Maßgeschneiderte Schicht-Interfacesysteme mittels ionenstrahlgestützter Beschichtung (1998)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 518-524 
    Details
    ISSN: 0933-5137
    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: Custom-Tailored Coating-Interface Systems by Means of lon Beam Assisted DepositionA coated sample represents in its most simple form a threefold junction consisting of substrate interface and top layer. In many cases the top layer consists again of several sublayers or the interface contains a modified substrate surface and an interconnection between top layer and interface. An ideal coating technique is evaporation under simultaneous ion bombardment with an ion source it is possible because of several free parameters to come close to an ideal system.For the coating Al/Al2O3 on steel it is shown that the width of a composition gradient between the sublayers Al and Al2O3 can be optimized with respect to excellent corrosion resistance.The example CrxN coating on steel or corrosion and wear resistence demonstrate the ability to optimize the corrosion and wear resistence by modifying the microstructure via variation of the parameters ion energy, ion impact angle, ion to atom ratio and process temperature.Finally, TiN layers on steel were chosen to show that the ion beam parameters influence the porosity and the crystal structure of the coatings. This fact can be used to optimize the corrosion protection or wear reduction obtained by the coating. Especially the multilayer Ti/TiO2/TiN exhibits very interesting properties.
    Notes: Ein beschichtetes Bauteil stellt in seiner einfachsten Form einen Dreierverbund aus Substrat, Interface und Schicht dar, in vielen Fällen kann die Schicht aus mehreren Untersystemen bzw. das Interface aus der modifizierten Substatrandschicht und einem Zwischenbereich zur Schicht bestehen. Eine ideale Beschichtungsmethode sollte es daher erlauben, alle diese Schichten bzw. Schichtbereiche in kontrollierter und aufeinander abgestimmter Form zu erzeugen.Mittels des IBAd-Verfahrens, bei dem Aufdampfschichten während ihrer Abscheidung mit Ionen aus einer Ionenquelle beschossen werden, ist es möglich, infolge der zahlreichen frei wählbaren Parameter sich an das ideale System heranzutasten.Anhand des Verbunds Stahl/Al/Al2O3 wird erlätert, wie durch einen in der Ausdehnung optimierten Zusammensetzungsgradienten das Interface zwischen den Subschichten Al und Al2O3 bezüglich des Korrosionsschutzvermögens der Schicht verbessert werden kann.An CrxN-Schichten wird demonstriert, daß durch die Wahl der Parameter Ionenenergie, Ioneneinfallswinkel, Ionen/Atom-Verhältnis und Prozeßtemperatur über die Mikrostruktur von Schicht und Oberfläche das Verschleiß-und Korrosionsverhalten sowie die Härte angepaßt werden können.Am Beispiel TIN auf Stahl zeigt sich, daß je nach Ionenstrahlparameter die Porosität und damit das Korrosionsverhalten bzw. die Kristallinität und damit Härte und Verschleißverhalten optimiert werden können. Besonders Mehrlagenschichten Ti/TiO2/TiN zeigen interessante Eigenschaften.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19980290910
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  • 7
    Electronic Resource
    Electronic Resource
    Ionen- und plasmagestützte Verfahren der Oberflächentechnik für die Randschichtbehandlung von Leichtmetallwerkstoffen (1998)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 537-544 
    Details
    ISSN: 0933-5137
    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: Surface engineering of light weight materials with ion- and plasma-assisted methodsIncreasing applications of light weight materials are expected in the future. Pursuing this trend surface engineering of these materials - especially ion- and plasma-assisted methods - swill be of increasing interest to enhance their wear and corrosion resistance. In a research co-operation some promising methods were examined on different aluminium and titanium alloys to assess their potential to increase the surface properties. Among these were magnetron sputtering of chromium nitride, ion beam assisted deposition of Cr/CrN and Al/A2O3 layers, ion implantation and ion beam assisted nitriding. Compared to the steel substrates the assessment of the mechanical properties such as the critical load of the scratch test of the coated light weight materials is different. Furthermore, it could be shown that both spherical section and glow discharge optical spectroscopy are useful methods to characterize the near-surface zone influenced by ion implantation.
    Notes: Es ist zu erwarten, daß die Anwendungsbreite von Leichtmetall-legierungen in Zukunft noch steigen wird. Mit diesem Trend werden auch oberflächentechnische Methoden - insbesondere ionen- und plasmaunterstützte Verfahren - gefragt sein, um den Verschleiß- und Korrosionswiderstand der Oberflächen zu verbessern. Im Rahmen eines Verbundprojektes wurden verschiedene aussichtsreiche Verfahren untersucht, um ihr Potential zur Verbesserung der Oberflächeneigenschaften von Aluminium- und Titanlegierungen einschätzen zu können. Hierunter befanden sich das Magnetronsputtern von Chromnitrid, die ionenstrahluntersützte Abscheidung von Cr/CrN- und Al/A2O3Schichten, die Ionenimplantation und das Ionenstrahlnitrieren. Im Vergleich mit beschichteten Stahlsubstraten ergeben sich Unterschiede bei der Einschätzung wichtiger mechanischer Eigenschaften, wie der im Ritztest ermittelten kritischen Last. Weiterhin konnte gezeigt werden daß sowohl der Kalottenschliff als auch die Glimmentladungspektroskopie gut geeignet sind, die durch Ionenimplantation beeinflußte Randzone zu charakterisieren.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19980290912
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  • 8
    Electronic Resource
    Electronic Resource
    Neue Synthese von 4-AzaphenothiazinHerrn Dr. W. A. Schuler zum 80. Geburtstag gewidmet. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 591-592 
    Details
    ISSN: 0947-3440
    Keywords: Azaphenothiazine ; Smiles rearrangement ; Pyrido[3,2-b][1,4]benzothiazine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Synthesis of 4-AzaphenothiazineHerrn Dr. W. A. Schuler zum 80. Geburtstag gewidmet.The reaction of 2-chloropyridine with 2-aminothiophenol gives N-(2-mercaptophenyl)-2-pyridinamine (2) which is cyclised to give 4-azaphenothiazine (3), a useful intermediate for pharmaceuticals. An improved one-pot synthesis is reported and a reaction mechanism proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950381
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  • 9
    Electronic Resource
    Electronic Resource
    Beanspruchungsverhalten von PVD-CrN Beschichtungen auf Leichtmetallwerkstoffen (1998)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 9-15 
    Details
    ISSN: 0933-5137
    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: Behaviour of light metals with PVD-CrN coatings using different test methodsThe application of thin hard coatings on machining tools, e.g. drilling tools is state of the art. The increase of lifetime of coated Tools compared to uncoated tools is well known. [1]. In this context „separation of functions“ is an often used phrase, by meaning the separation of functions of the volume and the surface of materials. Going one step forward, from the point of view of tribology or corrosion this means, you have „only“ to protect the surface by using a „good“ coating without looking at the material underneath. In the past the influence of substrate materials or the optimization of the system (substrate-coating) was not the main aim of PVD development. Looking at substrate and coating as a system is especially necessary, if the differences of the properties of substrate and coating are large (e.g. hard coating - light metals).This paper shows different aspect of the tribological and electrochemical characterization of PVD coated light metals (CrN coating).
    Notes: Das Aufbringen dünner Hartstoffschichten ist bei tribologisch stark beanspruchten Werkzeugen, wie z. B. bei Dreh- und Umformwerkzeugen., Stand der Technik. Standzeiterhöhungen der beschichteten Werkzeuge im Vergleich zu unbeschichteten Referenzen sind vielfach bestätigt [1].In diesem Zusammenhang ist in vielen Fällen „Funktionstrennung“d. h. eine Trennung der Aufgaben von Werkstoffvolumen und Werkstoffoberfläche, ein zentrales Schlagwort. Dabei wird davon ausgegangen, daß tribologische und korrosive Beanspruchungen nur auf Oberflächen wirken und darum nur diese mit einer geeigneten Schicht zu schützen sind. Die Wahl der Substratwerkstoffe oder eine Optimierung des Schicht-Substrat-Verbundes stand oft nicht im Mittelpunkt der PVD - Schichtentwicklung. Betrachtungen zum Schicht-Substrat-Verbund sind jedoch unumgänglich, wenn die Eigenschaften von Schicht und Substrat stark von einander abweichen (z. B. Hartstoffe auf „weichen“ Leichtmetallen im Gegensatz zu Hartstoffen auf hochfesten Stahlsubstraten).Der Beitrag greift wesentliche Aspekte zur mechanisch-tribologischen und elektrochemischen Bewertung hartstoffbeschichteter Leichtmetalle am Beispiel PVD-CrN auf.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19980290105
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  • 10
    Electronic Resource
    Electronic Resource
    Polycations. II. Chiral ammonium dendrimer synthesisFor Part I in this series, see Ref. [1a]. (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 9 (1998), S. 485-494 
    Details
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and investigation of chiral cationic dendrimers is described. In these species, cationic sites are provided by quaternary ammonium ion centers derived from the dinitrogen compound 1,4-diazabicyclo[2.2.2]octane (dabco). Stereogenic sites within the dendrimer structures are provided by derivitization of the readily available (S)-1,2,4-butanetriol. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 485-494, 1998
    Additional Material: 3 Ill.
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