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  • electroconduction  (1)
  • electron transfer  (1)
  • ethylene/1-butene copolymers  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Stilbene-containing liquid crystalline side chain homo- and copolysiloxanes: Microphase separation and chemical modification to electroconducting materials (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 39 (1996), S. 37-46 
    Details
    ISSN: 0959-8103
    Keywords: side chain polysiloxanes ; stilbene ; electroconduction ; electron hopping ; liquid crystal polymers ; microphase separation ; 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 phase behaviour of two classes of side chain polysiloxanes, containing respectively 4-cyano- and 4-alkoxy-4′-stilbene-ether mesogens, was studied over a wide temperature range by differential scanning calorimetry and wide angle X-ray diffraction, with special attention devoted to the characterisation of the microdomain phase morphology. Room temperature X-ray diffraction studies suggest for certain polymers with cyanostilbene mesogens the occurrence of microphase separation; this effect becomes significant as the amount of polysiloxane backbone versus the side chains increases. The onset of electrical conductivity was followed upon exposure of the polymeric films to various doping agents; conductivities up to 2 × 10-1 S cm-1 were measured when cyanostilbene-containing polymers were exposed to strong Lewis acids such as SO3 or SbF5. However, occurrence of some chemical degradation upon heavy doping and of electrode polarisation during DC conductivity measurements indicate that the observed electroconductivity is not purely electronic.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Electron transfer mechanism in olefin polymerization (1995)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 159-167 
    Details
    ISSN: 1042-7147
    Keywords: transition metal catalyst ; olefin polymerization ; electron transfer ; polymerization mechanism ; 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: Polymerization of olefins mediated by transition metal derivatives (Ziegler-Natta polymerization) is one of the most scientifically and industrially important processes of molecular conversion. Electron transfer mechanism could play a significant role in both heterogeneous and homogeneous catalysts. The catalytic activity strongly depends on the presence of two metallocene ligands attached to the transition metal (more commonly zirconium) which grants the valence form of zirconium in complexes of the type Cp2ZrX2(X=Cl or CH3) followed by the formation of the (Cp2ZrX)+ cation under the effect of a Lewis acid. On the other hand, Ti complexes with only one metallocene ligand give the syndiospecific polymerization of styrene, where the phenyl group appears to act as electron donor for the transition metal. The remarkable electronic effect of the metallocene groups in determining catalytic activity is demonstrated by the study of substituted metallocene ligands as well as other ligands around the metal. These effects cannot be, however, completely separated from steric effects which seem to be responsible for the impressive and versatile stereochemical control determined by symmetry properties of the transition metal complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1995.220060310
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    DSC analysis of ethylene/1-butene copolymers obtained with different ziegler-natta catalysts (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 33 (1994), S. 279-284 
    Details
    ISSN: 0959-8103
    Keywords: ethylene/1-butene copolymers ; Ziegler-Natta catalysts ; sequence distribution ; thermal properties ; 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 crystallization and melting behaviour of two sets of ethylene/1-butene copolymers have been analysed by DSC. The samples, with comonomer content in the range from 0 to 21.5 mol%, were obtained by industrial processes using both Mg/Ti-based catalyst systems. The composition dependences of melting and crystallization temperatures were found to be strictly affected by the catalyst type. Moreover, logarithmic plots of the melting and crystallization enthalpy as a function of the ethylene content (mol%) in the copolymers fitted linear relationships whose slopes have been related to the critical sequence length of crystallizable ethylene units, depending on the catalytic system. These results are compared with those reported in the literature for ethylene/1-butene copolymers synthesized by other catalysts and are accounted for by a different distribution of the comonomer units in the macromolecules of the two sets of samples.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1994.210330307
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    Paper (German National Licenses)
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