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  • 1
    Electronic Resource
    Electronic Resource
    Dielectric relaxation of LC-thermotropic poly(ester imide)s (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 203-212 
    Details
    ISSN: 0887-6266
    Keywords: poly(ester-imide)s ; liquid crystalline polymers ; dielectric relaxation ; model calculations ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two different series of poly(ester imide)s, which are distinguished from each other in the orientation of the ester linkages and show well-differentiated thermotropic behavior, are investigated by means of model calculations and dielectric relaxation spectroscopy. Model calculations show that the orientation of the ester linkages has a strong influence on the rotational energy barriers. The dielectric relaxation spectra of both series shows three relaxation regions in the temperature range between 100 and 400 K that have been identified as the α-, β- and γ-relaxation processes. A difference of about two orders of magnitude between the characteristic rates of the γ-relaxation is the main feature observed in the dielectric response. However, the β-relaxation shows very similar behavior for both series. The differences in the relaxation behavior in the solid state are interpreted on the basis of the rotational barriers deduced from the model calculation results. © 1997 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Relaxation behavior of aliphatic-aromatic poly(ether amide)s as revealed by dynamic mechanical and dielectric methods (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 457-468 
    Details
    ISSN: 0887-6266
    Keywords: poly(ether amide)s ; mechanical relaxation ; dielectric relaxation ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanical and dielectric relaxation of a set of aromatic-aliphatic polyamides containing ether linkages have been examined as a function of temperature (-140 to 190°C) and frequency (3 to 106 Hz). The polymers differ in the orientation (meta and para) of the aromatic rings, in the length of the aliphatic chain, and in the number of ether linkages per repeating unit. Dynamic mechanical experiments showed three main relaxation peaks related to the glass transition temperature of the polymers (α relaxation), the subglass relaxations associated to the absorbed water molecules (β) and to the motion of the aliphatic moieties (γ). Dielectric experiments showed two subglass relaxation processes (β and γ) that correlates with the mechanical β and γ relaxations, and a conduction process (σ) above 50°C that masks the relaxation associated to the glass transition. A molecular interpretation is attempted to explain the position and intensity of the relaxation, studying the influence of the proportion of para- or meta- oriented phenylene rings, the presence of ether linkages and the length of the aliphatic chain. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 457-468, 1997
    Additional Material: 10 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Dielectric relaxation studies of aromatic polyamides (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 919-927 
    Details
    ISSN: 0887-6266
    Keywords: dielectric relaxation ; aromatic polyamides ; rotational barrier ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric relaxation spectroscopy (DRS) is presented for a family of four aromatic polyamides trying to relate the structure of the lateral groups to the molecular mobility. A prominent sub-Tg absorption is always seen followed in some cases by remanent dielectric activity at room temperature and a subsequent increase of the loss permittivity. The low temperature relaxation is analyzed in terms of a Fuoss-Kirkwood equation to obtain the broadness and the strength of these relaxations as well as the activation energy (ranging from 10 to 11 Kcal/mol). The low frequency conductive peak shows in each case a half-width higher (1.30) than those corresponding to a single relaxation time peak (1.144). These values of the half-width are an indication of the complex character of these phenomena. A final discussion of the rotational barriers of the lateral chains rules out that such motions are the only molecular origin for the gamma relaxation. Instead, some kind of motion involving the main chain and where the interchain interactions play a significant role should be considered as responsible for that relaxation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 919-927, 1997
    Additional Material: 9 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    On the form IV of syndiotactic polypropylene (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 395-402 
    Details
    ISSN: 0887-6266
    Keywords: syndiotactic polypropylene ; form-IV ; form II ; kink bands ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The packing of the chains in (T6G2T2G2)n conformation of the form IV of s-PP is revisited on the basis of packing energy and structure factor calculations. According to this analysis, an alternative mode of packing has been suggested. A monoclinic structural model, with the unit cell centered on the C face, is obtained, after small changes of the atomic coordinates in the triclinic structural model as proposed by Chatani et al. The monoclinic model presents a lower packing energy than the triclinic model and a good agreement between the calculated and observed structure factors. The triclinic structural model implies that all the chains are rotated by the same amount around the chain axis with respect to the monoclinic structural model. Since clockwise and counter clockwise rotations are equivalent, the monoclinic structural model may be taken as descriptive of the order in the long range, for the form IV of s-PP, or in other terms, descriptive of an average structure (space group C2, unit cell constants equal to am = 14.17 Å, bm = 5.72 Å, cm = 11.6 Å, and βm = 108.8°). The triclinic structural model for this polymorph, instead (space group P1, unit cell constants equal to at = 5.72 Å, bt = 7.64 Å, ct = 11.60 Å, αt = 73.1°, βt = 88.8°, γt = 112.0°) is probably more properly descriptive of local situation of order (the symmetry, locally, is broken). Analogies between the monoclinic limit ordered structural model for the form IV and the orthorhombic limit ordered structural model for the form II (with chains in the more stable (TTGG)n conformation) of s-PP are also provided. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 395-402, 1998
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    1,2,4- and 1,3,5-trivinylbenzenes. Vapor-phase chromatographic and nuclear magnetic resonance characterization (1967)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 5 (1967), S. 1805-1806 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No Abstract
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1967.150050729
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  • 6
    Electronic Resource
    Electronic Resource
    Model compounds and polymers with quinoxaline units (1966)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 2831-2842 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetra- and heptanuclear N-heterocycles, their dimers and their polymers have been prepared by condensation of o-phenylenediamine or 3,3'-diaminobenzidine with 2,3-dihydroxyquinoxaline, 2,3,2,3'-tetrahydroxy-6,6'-bisquinoxaline, or 2,3,7,8-tetrahydroxy-1,4,6,9-tetraazaanthracene in polyphosphoric acid, or with the O-phenyl derivatives of the latter three compounds in phenol. The condensation products are highly colored compounds with characteristic absorption spectra. The polymers show good thermal stability.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1966.150041109
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  • 7
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    Friedreich's ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion (1996)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1996-03-08
    Description: Friedreich's ataxia (FRDA) is an autosomal recessive, degenerative disease that involves the central and peripheral nervous systems and the heart. A gene, X25, was identified in the critical region for the FRDA locus on chromosome 9q13. This gene encodes a 210-amino acid protein, frataxin, that has homologs in distant species such as Caenorhabditis elegans and yeast. A few FRDA patients were found to have point mutations in X25, but the majority were homozygous for an unstable GAA trinucleotide expansion in the first X25 intron.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Campuzano, V -- Montermini, L -- Molto, M D -- Pianese, L -- Cossee, M -- Cavalcanti, F -- Monros, E -- Rodius, F -- Duclos, F -- Monticelli, A -- Zara, F -- Canizares, J -- Koutnikova, H -- Bidichandani, S I -- Gellera, C -- Brice, A -- Trouillas, P -- De Michele, G -- Filla, A -- De Frutos, R -- Palau, F -- Patel, P I -- Di Donato, S -- Mandel, J L -- Cocozza, S -- Koenig, M -- Pandolfo, M -- 722/Telethon/Italy -- NS34192/NS/NINDS NIH HHS/ -- New York, N.Y. -- Science. 1996 Mar 8;271(5254):1423-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department de Genetica, University of Valencia, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8596916" target="_blank"〉PubMed〈/a〉
    Keywords: Alleles ; Amino Acid Sequence ; Base Sequence ; Chromosomes, Human, Pair 9/*genetics ; DNA Primers ; Female ; Friedreich Ataxia/*genetics ; Genes, Recessive ; Heterozygote ; Humans ; *Introns ; *Iron-Binding Proteins ; Male ; Molecular Sequence Data ; Pedigree ; Point Mutation ; Polymerase Chain Reaction ; Proteins/chemistry/*genetics ; Sequence Alignment ; *Trinucleotide Repeats
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 8
    Electronic Resource
    Electronic Resource
    Mechanical secondary relaxation effects in polysulfone (1967)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 5 (1967), S. 1296-1299 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1967.160050624
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  • 9
    Electronic Resource
    Electronic Resource
    Deformation, scattering, and birefringence of flexible polymer chains under external forces or electric fields (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 689-697 
    Details
    ISSN: 0887-6266
    Keywords: tensile force ; electric field ; chain conformation ; birefringence ; scattering ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of a tensile stress or an electric field on the conformation of a flexible polymer chain has been studied by combining theory with numerical simulation. In the presence of such external agents, the macromolecule experiences the action of two opposite forces at the chain ends. Two models are considered: the Gaussian bead-and-spring chain, and the freely jointed chain with segments of fixed length. From simulated Brownian trajectories we calculate steady-state properties of the polymer under the continuing action of the external forces. Thus, we compute the chain deformation and expansion, measured by the square radius of gyration, and analyze the influence of the external force on low-angle scattering of radiation. The effect of the link orientation in the optical anisotropy or birefringence is also analyzed. From existing theories, we predict very simple relationships between expansion, low-angle scattering, and birefringence, valid for Gaussian chains of any length, and for long freely jointed chains. The simulation results confirm those relationships. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 689-697, 1997
    Additional Material: 6 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Metastable liquid-liquid and solid-liquid phase boundaries in polymer-solvent-nonsolvent systems (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 763-770 
    Details
    ISSN: 0887-6266
    Keywords: melting transitions ; liquid-liquid demixing ; immersion precipitation ; membranes ; nonequilibrium phenomena ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In general liquid-liquid demixing processes are responsible for the porous morphology of membranes obtained by immersion precipitation. For rapidly crystallizing polymers, solid-liquid demixing processes also generate porous morphologies. In this study, the interference of both phase transitions has been analyzed theoretically using the Flory-Huggins theory for ternary polymer solutions. It is demonstrated that four main thermodynamic and kinetic parameters are important for the structure formation in solution: the thermodynamic driving force for crystallization, the ratio of the molar volumes of the solvent and the nonsolvent, the polymer-solvent interaction parameter, and the rate of crystallization of the polymer compared to the rate of solvent-nonsolvent exchange. An analysis of the relevance of each of these parameters for the membrane morphology is presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 763-770, 1997
    Additional Material: 6 Ill.
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