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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Spectrochimica Acta 18 (1962), S. 823-836 
    ISSN: 0371-1951
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Spectrochimica Acta 18 (1962), S. 823-836 
    ISSN: 0371-1951
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Theoretical Biology 104 (1983), S. 321-347 
    ISSN: 0022-5193
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-4846
    Keywords: CdSe nanocrystals ; silica xerogels ; sonogels ; SAXS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Small-angle X-ray scattering (SAXS) experiments were carried out to characterize the structure of the composite formed by CdSe nanocrystals embedded in a popous silica matrix (silica xerogels containing Cd with formamide addition and ultrasound treatment). SAXS results from samples before Se diffusion indicate the presence of heterogeneities with a bimodal size distribution which was associated to the existence of mesopores (pores of several hundred Å) immersed in a nanoporous matrix (characteristic pore radii of 20–30 Å). The diffusion of Se induces the nucleation and growth of CdSe nanocrystals. The average size of the nanocrystals increases with Cd content. Higher Se doses promote the formation of larger nanocrystals (radius of gyration of ∼30 to 50 Å). Anomalous scattering results confirm the existence of Se aggregation associated with CdSe nanocrystal formation and suggest that only partial segregation of Cd and Se occurs.
    Type of Medium: Electronic Resource
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  • 5
    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: Eine Reihe von urethan- und harnstoff- oder semicarbazid-verknüpften Polyethern für biomedizinische Anwendungen wurde katalysatorfrei hergestellt und systematisch auf mechanische Eigenschaften und Hydrolysierbarkeit untersucht. Besonders eingehend wurde wegen seiner überragenden Eigenschaften das System Poly(oxytetramethylen)diol (POTM)/4,4′-Diisocyanatodiphenylmethan (DDM) untersucht; die Polyether-Diisocyanate wurden mit ausgewählten Diaminen oder Dicarbonsäuredihydraziden umgesetzt. Das Molverhältnis DDM/POTM und die Art des Kettenverlängerers bestimmen die hydrolytische Stabilität. Die besten mechanischen Eigenschaften, gute Hydrolysebeständigkeit und gute Blutverträglichkeit zeigten Polyetherurethansemicarbazide.
    Notes: A series of urethane- and urea- or semicarbazide-linked polyethers for biomedical applications were synthesized without the use of a catalyst. Mechanical properties and hydrolyzability of the polymers were investigated. Due to its superior properties, the system poly(oxytetramethylene)diol (POTM)/4,4′-diisocyanatodiphenylmethane (DDM) was studied quite thoroughly. Its resistance against hydrolysis was determined by the molar ratio DDM/POTM and by the kind of chain extender. Polyetherurethane-semicarbazides showed the best mechanical properties, good resistance against hydrolysis and good blood compatibility.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    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: Die IR-Spektren von urethan-, harnstoff- und semicarbazid-verknüpften aliphatischen Polyethern (Poly(oxyethylene), Poly(oxytetramethylen) und Poly(oxypropylen)) wurden bei 300 K und 153 K gemessen. Die Zuordnung der verschiedenen Struktureinheiten zu bestimmten Gruppen von Absorptionsbanden (charakteristische Bandenkombinationen) geschah durch die Auswetung der Spektren von Vergleichssubstanzen und von Literaturwerten. Die bei tiefen Temperaturen auftretenden Effekte lassen sich nicht als das Auftreten von Kristallinität, sondern nur als beginnende Kettenregularität in den Poly(oxyethylen)- und Poly(oxytetramethylen)-Sequenzen deuten.
    Notes: The infrared spectra of urethane-, urea-, and semicarbazide-linked aliphatic polyethers (poly(oxyethylene), poly(oxytetramethylene) and poly(oxypropylene)) have been measured at 300 K and 153 K. The assignment of the different structural units to certain groups of absorption bands (“characteristic band combinations”) was made by the evaluation of the spectra of reference compounds and of literature data. The low-temperature effects (band splitting, shift of band maxima) facilitate the identification of structural units in these polymers. The observed effects do not signify crystallinity but beginning regularity of the poly(oxyethylene) and poly(oxytetramethylene) sequences.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 7
    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: Bismaleimides polymerize at elevated temperatures, forming highly crosslinked, high temperature-resistant polymers. From the decrease of the ν(H—C=) band at 3100 cm-1, rate constants and activation energies of the polymerization of four homologous aliphatic bismaleimides were determined. Up to a 20-30% conversion, the polymerization is pseudofirst order. An almost linear correlation between the activation energy and the number of methylene groups in the sequence between the maleimide residues was found.
    Additional Material: 7 Ill.
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  • 8
    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: The introduction of computer-assisted IR and FTIR spectrometers has greatly enlarged the possibilities of qualitative and quantitative analysis of macromolecular multi-component systems. By using the digitally stored standard spectra of the components of a system the composition of this system can be evaluated under the condition that spectral superposition is valid. Since this condition is frequently invalid it is preferable, for the analysis of a system with n spectroscopically defined components, to choose n compositions within an optimal range within the (n  -  1) dimensional Gibbs diagram. In real polymer blends with crystallizable components the degree of crystallinity of these components will be lower than in the unmixed polymers. This is probably due to the mutual interpenetration of the noncrystalline ranges of the different polymers. Highly filled materials can be identified quite reliably when the filler or reinforcing material is monodisperse. This ist the case, e.g., with dental cements (fillings). Organically filled construction materials with low concentrations of binder (e.g., fiber board) can be identified by difference spectrometry when the characteristic absorptions of the binder will not coincide with strong bands of the filler.  -  Artefacts may falsify a difference spectrum. Origins and consequences of artefacts will be discussed.
    Notes: Die Einführung computerunterstützter IR- und FTIR-Spektrometer hat die Möglichkeiten der qualitativen und quantitativen Analyse von makromolekularen Mehrkomponentensystemen erheblich erweitert. Wenn die Forderung der spektralen Superposition erfüllt ist, läßt sich mit Hilfe gespeicherter Standardspektren der Komponenten durch Differenzspektrometrie die Zusammensetzung eines Systems ermitteln. Da diese Forderung sehr oft nicht erfüllt ist, wählt man für die Differenzspektrometrie eines Systems aus n spektral definierten Komponenten n Punkte aus dem empirisch zu ermittelnden optimalen Bereich im Innern des (n-1)-dimensionalen Gibbsschen n-Ecks. Bei realen Polymergemischen mit kristallisierbaren Komponenten ist deren Kristallinitätsgrad niedriger als in den ungemischten Polymeren; dies ist wahrscheinlich auf gegenseitige Durchdringung der nichtkristallinen Bereiche zurückzuführen. Hochgefüllte Kunststoffe lassen sich differenzspektrometrisch noch gut identifizieren, wenn der Füllstoff monodispers ist (Zahnzemente). Organisch gefüllte Werkstoffe mit niederem Bindemittelanteil (Hartfaserplatten mit Holzschliff) lassen sich nur dann differenzspektrometrisch identifizieren, wenn die charakteristischen Absorptionen des Bindemittels in Bereichen liegen, in denen der Füllstoff nicht stark absorbiert.  - Artefakte können ein differenzspektrometrisches Ergebnis verfälschen. Ursachen und Auswirkungen von Artefakten werden diskutiert.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0570-0833
    Keywords: Emulsion polymerization ; Polymerization ; Polymerization ; Alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ionizing radiation induces the polymerization of some vinyl monomers in aqueous emulsion with high radiation yields. With identical emulsion compositions, the kinetics of this reaction and the kinetics of emulsion polymerization induced by water-soluble initiators are very similar. The rate of reaction in emulsion polymerization is about one hundred times greater than in bulk polymerization. The initiation of emulsion polymerization by means of ionizing radiation permits uniform “illumination” of the reacting volume, as well as almost any desired variation in the frequency of initiation during the reaction. The sharp decrease in the overall rate of reaction when initiation is interrupted during emulsion polymerization of styrene induced by γ-rays contradicts the earlier concept of sharply separated reaction zones.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The orientation capability of thin solution-cast films of a new synthesized crosslinkable thermotropic main chain copolyesterwith itaconoyl units was demonstrated by means ofpolarized FTIR spectrometry. The isotropic films with a thickness of about 10 μm were drawn uniaxially and annealed to get a preferential alignment of the polymer backbone in the drawing direction and an increase of the state of order. The resulted state should be fixed by a following crosslinking reaction of the itaconoyl unit to obatin a thermostable polymeric material with reduced anisotropy of mechanical properties. The orientation effects of mesogenic units dominate in the drawn films of the ternary copolyester. WAXS and DSC results show that annealing of the films produce an increase in crystallinity. More ordered regions in the solid polymer are formed which cause typical changes in the IR spectra.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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