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  • Polymer and Materials Science  (9)
  • phase separation  (1)
  • random copolymers  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Spin lattice relaxation in linear polyethylene (1969)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 1165-1186 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The proton spin-lattice relaxation times (T1) of linear polyethylenes (PE) of varying morphology were measured as a function of temperature. The T1 of oriented bulkcrystallized and solution-crystallized material was isotropic, in disagreement with calculations based on a sample dipole pair model. Motion in the non-crystalline regions of the samples is shown to be responsible for the T1 minimum occurring around -20°C. The dependence of T1 at the minimum on the long period reinforces the model of an amorphous fraction composed of disordered lamellar surface layers. The temperature of the T1 minimum and the dependence of T1 on the long period imply that the mobility of these amorphous regions is reduced in cold-drawn and solution-crystallized samples. This mobility irreversibly increases with annealing. In highly relaxed samples the motion of a small portion of the disordered regions is almost liquidlike, as indicated by the presence of a second shorter T1.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1969.160070703
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  • 2
    Electronic Resource
    Electronic Resource
    The Physics of Polymers. By G. R. Strobl, Springer, Berlin 1996, xii, 439 pp., softcover, DM 54.00, ISBN 3-540-60788-4 (1997)
    Weinheim : Wiley-Blackwell
    Advanced Materials 9 (1997), S. 277-277 
    Details
    ISSN: 0935-9648
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/adma.19970090327
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  • 3
    Electronic Resource
    Electronic Resource
    Spin-lattice relaxation from endgroups in atactic polystyrenes (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 1719-1724 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.160090913
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  • 4
    Electronic Resource
    Electronic Resource
    Concentration and chain-length dependence of thermodynamic interactions in polyethylene isotope blends (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2889-2899 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; polyolefins ; blends ; thermodynamics ; neutron scattering ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Small-angle neutron scattering (SANS) measurements of interactions in polymer blends, χNS, generally depend on blend concentration Φ, even though χNS is evaluated with a model that assumes that the thermodynamic interaction parameter χFH = χNS is independent of Φ. Londono et al. have reported χNS to increase by ∼ 4× when Φ drops below 0.05 in polyethylene isotope blends. The relation between scattering and thermodynamics is addressed with incompressible Flory-Huggins theory wherein the nthermodynamic interaction parameter χ may vary with concentration Φ and degree of polymerization N; here χNS(Φ) ≠ χ(Φ). For polyethylene isotope and similar polyolefin blends, the strong upward curvature of χNS implies a modest (ca. 30%) increase of χ. Macroscopic phase behavior is unaffected because the shape of the binodal remains essentially unchanged. The Φ-dependence of χNS in turn depends on N, leading to the following empirical expression for the thermodynamic interaction parameter: χ(Φ, N) = β - (2γ′/NΦ1Φ2)(Φ1 ln Φ1 + Φ2 ln Φ2). For polyethylene isotope blends at 155°C, β = 2.85 × 10-4 and γ′ = 0.15. Simple Flory-Huggins behavior with χFH = β is recovered when N approaches infinity. The source of the Φ- and N-dependent second term is not known. © 1997 John Wiley & Sons, Inc. J Polym Phys 35: 2889-2899, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chain dimensions in plastically deformed semicrystalline polymers (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 859-874 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of plastic deformation on the chain dimensions of polymers in the semicrystalline state was investigated using linear hydrogenated polybutadiene (HPB), a model ethylene/butene-1 copolymer having about 40% crystallinity at room temperature. Dilute blends of deuterium-labeled chains with various molecular weights (20,000 ≤ M ≤ 214,000) in the same unlabeled matrix (M = 95,000) were uniaxially stretched at 25°C to extension ratios of α = 2.4 and 4.4. Radius of gyration normal to the stretch direction R⊥ was measured for the labeled chains by small-angle neutron scattering. The molecular extension ratio inferred from these data αm = Rg2/R⊥2 was significantly smaller than α for short chains (M 〈 50,000) but increased to the affine range αm = α for M 〉 100,000. This variation in αm/α closely parallels the molecular weight dependence of mechanical strength and ductility in HPB over the same range.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090270410
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  • 6
    Electronic Resource
    Electronic Resource
    Radiotherinoluminescence with in situ electron irradiation (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 1641-1645 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280917
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  • 7
    Electronic Resource
    Electronic Resource
    Recent developments in phase separation of polyolefin melt blends (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2329-2353 
    Details
    ISSN: 0887-6266
    Keywords: phase separation ; polyolefins ; neutron scattering ; random copolymers ; thermodynamics ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Saturated hydrocarbon polymers may be differentiated by the relative amount and placement of methylene, methyl, methine, and quaternary carbon moieties. While it has been known or suspected for some time that polyolefins of conventional molecular weight (Mw ≈ 100 kg/mol) with dissimilar chemical microstructures are most often immiscible in the liquid state, recent experiments with binary blends of model polyolefins have increased greatly our understanding of thermodynamic interactions between unlike chains. Model systems with methyl (-CH3) and ethyl (-C2H5) short-chain branches give results, expressed as the Flory-Huggins interaction parameter χ, that are nearly universal; repulsive interactions (χ 〉 0) are more pronounced at low temperatures, leading to liquid-liquid phase separation at an upper critical solution temperature. Phase behavior of more complex systems (with distributions of chain microstructures and/or molecular weight) is generally consistent with predictions from model systems. An interesting exception is from work at Bristol on blends of lightly branched ethylene - α-olefin copolymers with unbranched polyethylene as the minority species. Here the presence of two liquid phases is inferred under conditions not expected from model studies; effects of copolymer composition and molecular weight are also unusual. Recent theoretical work points to the importance of chain stiffness (established by short-chain branching) in determining the thermodynamics of model blends. Nonrandom mixing of chains with different stiffness gives rise to an enthalpic χ, which may be negative under certain conditions. Other limitations of the Flory-Huggins approach to describing blend energetics are considered. At present there is no theoretical basis for liquid-liquid phase separation reported by the Bristol group. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2329-2353, 1997
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular orbital studies of polyethylene deformation (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 449-457 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene ; elastic modulus ; molecular orbital ; ab initio ; semiempirical ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Young's modulus E for polyethylene in the chain direction is calculated with molecular orbital theory applied to n-alkanes C3H8 through n-C13H28 and analyzed with the cluster-difference method. Semiempirical CNDO, MNDO, and AM1 models and ab initio HF/STO-3G, HF/6-31G, HF/6-31G*, and MP2/6-31G* models are used. Cluster-difference results, when extrapolated to infinite chain length, give E in good agreement with moduli evaluated with molecular cluster or crystal orbital methods, provided minimal basis sets are employed. E decreases from 495 GPa (CNDO) to 336 GPa (MP2/6-31G*) as the level of theory is improved, consistent with established behaviors of the various models. Our calculations do not reproduce earlier molecular cluster or crystal orbital results, which gave E 〈 330 GPa. The most rigorous MP2/6-31G* model is known to overestimate force constants by ∼ 11%; the scaled modulus E = 299 GPa is in good accord with E = 306 GPa from recent calculations based on experimental vibration frequencies. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Small-angle x-ray scattering of semicrystalline polymers. I. Review of existing models (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 635-661 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of previously proposed distributions of particle size and interparticle “gap” lengths on the small-angle x-ray scattering of a paracrystalline one-dimensional macrolattice has been examined. It was concluded that the general paracrystalline model, in which the fluctuations of crystalline and amorphous thickness both contribute to the destruction of long-range order, best describes the structure of lamellar aggregates in semicrystalline polymers. By using this model, the influence of symmetric and asymmetric lattice statistics on the positions of the scattering maxima were investigated. It was found that positively skewed thickness distributions result in the second-order maximum occurring at an angle greater than twice that of the first-order maximum (sx̄2/sx̄1 〉 2.0); the position of the first-order maximum is generally greater than the Bragg angle of the structure. With negatively skewed distributions, the ratio of the scattering angles, sx̄2/sx̄1, is less than 2.0, and the first maximum is displaced below the Bragg angle. Qualitatively similar behavior is found with lattices characterized by symmetric lattice statistics, though these deviations from the Bragg conditions are smaller than in the case of negatively skewed distributions. The ratio of the scattering angles of the second and first maxima best reflects the general shape of the lattice statistics in a paracrystalline lattice. The effect of a transition zone, having properties intermediate between those of the crystalline and amorphous regions, was also considered. While the intensity of the higher-order maxima is decreased, no significant shift of the scattering angles results from the incorporation of such a transition zone.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.180110403
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