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  • Chemistry  (5)
  • Computer Systems
  • 1990-1994  (5)
  • 1935-1939
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  • 1992  (5)
  • 1
    Electronic Resource
    Electronic Resource
    On the nature of order in wholly aromatic liquid crystalline random copolymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 1375-1385 
    Details
    ISSN: 0887-6266
    Keywords: liquid crystalline aromatic copolymers, solid state order in ; copolymers, wholly aromatic, nature of order in solid state of ; solid state order in aromatic liquid crystalline random copolymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two different models of order in the solid state of wholly aromatic liquid crystalline copolymers (ALCPs), namely the nonperiodic layer (NPL) model of Windle et al. and the paracrystalline lattice (PCL) model of Biswas and Blackwell, have been analyzed with respect to experimental and theoretical observations. The NPL model proposes the formation of ordered domains by matching random sequences between adjacent chains while the PCL model relies on the presence of conformational correlations between adjacent monomers, without explicit sequence matching, to form ordered domains. The presence of three-dimensional order in the quenched state of ALCPs has been reported previously. The initial stages of crystallization are very likely to be assisted by the presence of small sequence matched domains. However, the probabilities for the formation of NPL domains having sizes comparable to those observed experimentally in the quenched state are extremely small. The PCL model, on the other hand, is not hampered by probability statistics and also provides a better fit to the experimental wide-angle x-ray scattering data along the fiber (Z) axis. The reported calorimetric data on ALCPs are also inconsistent with the presence of significant motion between chains, which is required for the NPL crystal to grow during the process of annealing. In contrast, the observation of a slow crystallization process, which converts the quenched hexagonal phase to the ordered orthorhombic phase, is adequately described by the PCL model as occurring via local conformational changes and small axial shifts between adjacent monomers. The observations from dielectric relaxation, nuclear magnetic resonance and dynamical mechanical spectroscopy studies also favor the PCL model over the NPL model of order in the solid state of ALCPs. © 1992 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090301208
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and thermal stability, dielectric, and conductivity characteristics of some carbazole-bearing pendant and backbone sulfones (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 1685-1692 
    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: A group of poly(N-vinylcarbazole) pendant polysulfones has been prepared by reacting it with benzene, toluene, p-chlorobenzene- and p-nitrobenzenesulfonyl chloride and N-methyl carbazole, 3,6-disulfonyl chloride by the Friedel Crafts reaction. Carbazole-based backbone polysulfones have also been prepared by the reaction of N-methyl carbazole, 3,6-disulfonyl chloride and biphenyl, naphthalene, anthracene, and carbazole in presence of anhydrous aluminum chloride. The various sulfone polymers, thus prepared, have been structurally characterized by elemental analysis and IR spectroscopy. Detailed analyses of thermal stability, dielectric, and conductivity characteristics have revealed certain significant differences between these two types of sulfone polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070451001
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  • 3
    Electronic Resource
    Electronic Resource
    SAXS investigations on chiral liquid crystalline polymers: antiferroelectric and ferrielectric structures? (1992)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 3 (1992), S. 257-262 
    Details
    ISSN: 1042-7147
    Keywords: Chiral liquid crystalline polymers ; Antiferroelectricity ; Ferrielectricity ; SAXS ; 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
    Notes: The structure and phase behavior of liquid crystalline polymers (LCPs) having a common chiral side chain mesogen but different main chain structures have been investigated using small-angle X-ray scattering (SAXS). While the low molecular weight chiral side chain mesogen by itself exhibits ferroelectricity, the SAXS data of the side chain LCP with a flexible polyacrylate backbone contains a bilayered superstructure peak that is indicative of antiferroelectric order. The combined LCP with a nonpolar main chain mesogen also has a bilayered superstructure, but has a different structural organization in the proposed antiferroelectric phase compared to the side chain LCP. Further changes in the phase behavior and structural organization occur when a polar group is introduced into the main chain mesogen. A ferrielectric phase has been proposed to explain the observation of a trilayered superstructure in the corresponding SAXS data. The influence of the chemical structure and connectivity on the phase behavior and superstructure formation in the chiral LCPs is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1992.220030510
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  • 4
    Electronic Resource
    Electronic Resource
    Modification of styrene-divinylbenzene copolymer by anchoring ferric-dipyridylamine complex (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 1453-1460 
    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: Polystyrene-divinylbenzene (PS-DVB) copolymer was modified by anchoring dipyridylamine (DPA) on it followed by complexation with Fe(III). Under the experimental conditions followed, 9% incorporation of Fe(III) was achieved. PS-DVB-DPA and PS-DVB-DPA-Fe(III) were characterized by IR spectra. Diffuse reflectance spectra for PS-DVB-DPA-Fe(III) and DPA-Fe(III) revealed λmax at ∼ 360 and ∼ 310, respectively. This difference could be due to a difference in the nature of the coordinating moieties complexing with Fe(III) in these two systems. Scanning electron micrographs of PS-DVB, PS-DVB-DPA-Fe(III), and heat-treated PS-DVB-DPA-Fe(III) revealed some typical surface features. Thermal stability varied in the order PS-DVB-DPA-Fe(III) 〉 PS-DVB-DPA ≅PS-DVB, and DTA showed characteristic exotherms. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070460816
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  • 5
    Electronic Resource
    Electronic Resource
    Some observations on morphology of anhydride-modified polystyrene (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 44 (1992), S. 619-621 
    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: Friedel-Crafts acylation reaction between polystyrene and phthalic anhydride in the presence of AlCl3 has been performed in two different solvents, 1,2-dichloro ethane and nitro-benzene. The morphology of the condensate prepared in 1,2-dichloroethane has revealed the participation of 1,2-dichloroethane, i.e., a competitive Friedel-Crafts alkylation reaction.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070440407
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