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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 24 (1990), S. 9-16 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The synthesis and characterization of copolyethers based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE), 1,8-dibromooctane and each of the following three nonmesogenic bisphenols: 3,4′-dihydroxydiphenylmethane (3,4′-BPM), 4,4′-isopropylidenediphenol (4,4′-BPA) and 3,4′-isopropylidenediphenol (3,4′-BPA) are presented. Copolymers based on MBPE, 3,4′-BPM and 1,8-dibromooctane display a nematic mesophase up to compositions containing as much as 70 mol% of 3,4′-BPM. The range of mesomorphism decreases on going from 3,4′-BPM to 3,4′-BPA and to 4,4′-BPA. These results demonstrate that structural units derived from parent amorphous and liquid crystalline homopolymers can be isomorphous within the mesophase over a certain range of copolymer composition of the resulting copolymers. Subsequently, the parameters of the mesomorphic phase transitions of these copolymers represent weight averaged values of the corresponding parameters of the parent homopolymers.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 22 (1989), S. 489-496 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper describes the synthesis and characterization of the polyether based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl) ethane (MBPE) and 1,13-dibromotridecane (MBPE-13) and of the copolyethers based on MBPE and 1,13-dibromotridecane with 1,5-dibromopentane (MBPE-5/13), 1,7-dibromoheptane (MBPE-7/13), 1,9-dibromononane (MBPE-9/13), and 1,11-dibromoundecane (MBPE-11/13). MBPE-13 is only crystalline while all copolymers display two monotropic nematic mesophases. The virtual averaged isotropicnematic transition temperature of MBPE-13 determined from these copolymers is 70±3 °C (ΔH=1.63±0.24 kcal/mru), while the virtual nematic-nematic transition temperature is 60±6 °C (ΔH=0.03±0.02 kcal/mru).
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 22 (1989), S. 497-504 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The synthesis and determination of virtual mesomorphic phase transitions of the polyether based on l-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl) ethane (MBPE) and 1,14-dibromotetradecane (MBPE-14) and of the copolyethers based on MBPE and 1,14-dibromotetradecane with 1,5-dibromopentane (MBPE-5/14), 1,8-dibromooctane (MBPE-8/14) and 1,9-dibromononane (MBPE-9/14) are presented. The homopolymer MBPE-14 is only crystalline, while the copolymers display a monotropic (MBPE-5/14 and MBPE-9/14) or even an enantiotropic (MBPE-8/14) nematic mesophase. The averaged virtual isotropicnematic transition temperature of MBPE-14 determined from these copolymers is 87 ± 7 °C (ΔH=2.77±0.21 kcal/mru).
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 23 (1990), S. 225-232 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper describes the synthesis and characterization of the polyethers based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl) ethane (MBPE) and 1,15-dibromopentadecane (MBPE-15), MBPE and 1,16-dibromohexadecane, and of the copolyethers based on MBPE and 1,8-dibromooctane with 1,15-dibromopentadecane (MBPE-8/15), and with 1,16-dibromohexadecane (MBPE-8/16). MBPE-15 and MBPE-16 are only crystalline while MBPE-8/15 and MBPE-8/16 display a monotropic or even an enantiotropic nematic mesophase. The virtual isotropic-nematic transition temperature of MBPE-15 determined from these copolymers is 62°C (ΔH=2.58 kcal/mru), while the virtual isotropic-nematic transition temperature of MBPE-16 is 73°C (ΔH=3.15 kcal/mru).
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Styrol wurde in Methylenchlorid mit Mineralsäure, wie Schwefelsäure und Chlorwasserstoff, als Katalysator polymerisiert. Diese beiden Katalysatoren geben bei tiefer Temperatur Polymere von hohem Molekulargewicht. Wasser inhibiert die Polymerisation, was vielleicht der Bildung des H3O+ -Ions zuzuschreiben ist, das keine Polymerisation initiiert. Dies unterscheidet sich von der Polymerisation mit FRIEDEL-CRAFTS Katalysatoren, wo Wasser die Rolle eines Cokatalysators besitzt. Es wird angenommen, daß sich durch die Übertragung des Protons von H3SO4+ oder CH2Cl2H+ auf Styrol ein Carboniumion bildet, das die Polymerisation auslöst.
    Notes: Styrene was polymerized methylene chloride by hydrogen acid catalysts such as sulfuric acid and hydrogen chloride. Both catalysts give polymers of high molecular weight at low temperature. Water inhibits the polymerization, which may be due to the formation of H3O+ incapable of initiating polymerization. It contrasts with the polymerization by FRIEDEL-CRAFTS catalysts, where water behaves as a co-catalyst. It was considered that a carbonium ion may be generated by the transfer of proton from H3SO4+ or CH2Cl2H+ to styrene monomer and the polymerization may proceed by resultant carbonium ion.
    Additional Material: 2 Ill.
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  • 6
    ISSN: 1432-1424
    Keywords: surface charge ; surface concentration ; calcium channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Calcium ions affect the gating of Ca currents. Surface charge is involved but to what extent is unknown. We have examined this, using isolated nerve cell bodies ofHelix aspersa and the combined microelectrode-suction pipette method for voltage-clamp and internal perfusion. We found that Ba and Sr currents produced by substitution of these ions for extracellular Ca ions are activated at less positive potentials than Ca currents. Mg ions do not permeate the Ca channel and changes in [Mg]0 produce shifts in the activation-potential curves that are comparable to the effects of changes in [Ba]0 or [Sr]0. Inactivation of Ba currents also occurs at less positive potentials. Perfusion intracellularly with EGTA reduced inactivation of Ca currents as a function of potential, but did not shift the inactivation-potential curve. Hence, Ca current-dependent inactivation which is blocked by intracellular EGTA probably does not involve a similar change of intracellular surface potential. The voltage shifts of activation and inactivation produced by extracellular divalent cations used singly or in mixtures can be described by the Gouy-Chapman theory for the diffuse double layer with binding (Gilbert & Ehrenstein, 1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential values and the Boltzman distribution, we have computed surface concentrations that predict the following experimental observations: 1) saturation of current-concentration relationships when surface potential is changing maximally; 2) the increase in peak current when Ca ions are replaced by Sr or Ba ions; and 3) the greater inhibitory effect of Mg onI Ba thanI Ca. Theory indicates that surface charge cannot be screened completely even at 1m [Mg]0 and thus that Ca channel properties must be evaluated in the light of surface charge effects. For example, after correction for surface charge effects the relative permeabilities of Ca, Ba and Sr ions are equivalent. In the presence of Co ions, however, Ca ions are more permeable than Ba ions suggesting a channel binding site may be involved.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 5 (1961), S. 104-107 
    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: A tracer study has been made of the polymerization of acrylonitrile in an aqueous solution at 25°C with the use of radioactive K2S352O8 and NaHS35O3 in a redox catalyst system. Persulfate and bisulfite give sulfate and sulfonate endgroups, respectively. The contents of these endgroups in the polymer were determined and the following empirical equation was derived: \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{[{\rm Sulfonate endgroups]}}}{{[{\rm Sulfate endgroups]}}} = 1 + 0.27\left\{ {\frac{{[{\rm NaHSO}_{\rm 3} ]}}{{[{\rm AN] [K}_{\rm 2} {\rm S}_{\rm 2} {\rm O}_{\rm 8} ]}}} \right\}^{1.5} $ \end{document} Sulfonate is the major endgroup under every condition of polymerization. A tentative discussion of the polymerization initiation reaction in this redox system is given in order to account for the above experimental results.
    Additional Material: 1 Ill.
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  • 8
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0006-291X
    Keywords: [abr] Ac; acetyl ; [abr] DCC; N, N'-dicyclohexylcarbodiimide ; [abr] DPPA; diphenylphosphorazidate ; [abr] HOBt; 1-hydroxybenzotriazole ; [abr] PCA; perchloric acid ; [abr] Plg; plasminogen ; [abr] Suc; succinyl ; [abr] Z; benzyloxycarbonyl ; [abr] pNA; p-nitroanilide ; [abr] t-Boc; tert-butyloxycarbonyl
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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