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  • Articles: DFG German National Licenses  (27)
  • Polymer and Materials Science  (27)
  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 15 (1976), S. 2465-2483 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The normal vibration frequencies of poly(L-alanine) and poly(L-alanylglycine) in the antiparallel chain-pleated sheet structure have been calculated, using the force field for polyglycine I from the previous paper (Biopolymers 15, 2439-2464) plus additional force constants for the methyl group. The agreement with observed ir and Raman bands is very good. This substantiates the excellent transferability of the force field, since polyglycine I was shown to have a rippled-sheet structure. The amide I and amide II mode splittings are very well accounted for by transition dipole coupling, showing that subtle structural differences are sensitively manifested through this mechanism.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 15 (1976), S. 1513-1528 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Raman spectra of native and solubilized feather keratin have been obtained, and the amide I and amide III regions have been analyzed by band resolution techniques. The amide I region of the native form indicates that at least 64% of the protein has an antiparallel chain pleated sheet structure, the remainder being unordered. For the solubilized keratin all of the protein is in an unordered state. The amide III region is not as easily analyzed into component contributions. Normal vibration analyses on N-acetyl-L-alanine-N-methylamide support the conclusion that the amide III region is not as satisfactory as the amide I region in characterizing unordered structures. Even in the latter case caution must be used, since the observed amide I band is an average over the conformational distribution in the particular unordered system.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1191-1209 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molar Kerr constants mK, molar refractions mR, and dipole moments μ are reported for the N-methylacetamides CX3CONHCH3 (X = H, CH3, F. CI, Br) and acetamides CX3CONH2 (X = H, F, Cl, Br). The components of the polarizability tensor α are deduced for N-methylacetamide and acetamide on the basis of the bond additivity approximation. This α is found to be considerably more anisotropic than was indicated in previous determinations by other methods. The data for N-methylacetamide were used to calculate mK, μ, and γ2 (anisotropy squared) of N-acetyl-N′-methylglycine amide and N-acetyl-N′-methyl-alanine amide as functions of the torsional angles (φ,Ψ). The statistical mechanical averages of mK, μ, and γ2 were calculated from conformational energies obtained by the methods of Scheraga.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 2019-2029 
    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 sample of commercial atactic polypropylene was extracted with ether and the residue extracted with boiling n-heptane. Six fractions of the heptane-soluble material, which is very similar to that obtained by heptane extraction of isotactic polypropylene, were obtained by stepwise addition of acetone to a solution in cyclohexane. Densities, melting points, and x-ray photographs of the fractions and the unfractionated material were obtained and infrared absorption spectra used to estimate tacticity. Molecular weights, determined by means of a vapor pressure osmometer, ranged from about 3000 to about 25,000. That of the fraction of highest molecular weight was in good agreement with a separate determination by means of osmotic pressure measurements. Separation in fractionation occurred in order of decreasing molecular weight and increasing crystallinity as estimated from densities and x-ray photographs. Tacticity also seems to increase with decreasing molecular weight. Melting points of the fractions were not entirely in the order expected from their molecular weights and estimated crystallinities, and it is possible that low DP isotactic material may be preferentially concentrated in the highest molecular weight fraction. It is emphasized that the unfractionated material may contain polymers possessing a range of order intermediate between those of purely atactic and purely isotactic polymer and that refractionation may be required in order to characterize the material completely.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 15 (1976), S. 2439-2464 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A force field has been refined for the antiparallel chain-rippled sheet structure of polyglycine I. Transition dipole coupling and hydrogen bonding are explicitly taken into account. Amide I and amide II mode splittings are well accounted for, the latter also providing a quantitative explanation of the amide A and amide B mode frequencies and intensities. In addition to predicting other features of the vibrational spectrum of polyglycine I, this force field is completely transferable to other β polypeptides, even though these have the antiparallel chainpleated sheet structure.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 7 (1997), S. 195-206 
    ISSN: 1057-9257
    Keywords: cubic silicon carbide ; morphology ; photoluminescence ; micro-Raman ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Optically transparent cubic SiC crystals were grown via atmospheric-pressure chemical vapour deposition (APCVD) on graphite substrates from methyltrichlorosilane (MTS) in hydrogen in a cold-wall RF induction furnace at temperatures from 1500 to 2000°C. The morphology of the crystals was correlated to substrate temperature, H2/MTS ratio and hydrogen flow. Low-temperature photoluminescence (PL) spectra exhibited a zero-phonon line (2.3787 eV) attributable to an exciton bound to a neutral nitrogen donor, in addition to TA, LA, TO, and LO phonon replicas. The observed broadening and splitting of the PL spectral lines were associated with the morphological habit and internal strain of individual crystallites.Above about 1600°C preferential 〈110〉 growth directions were identified for the majority of the crystals. At intermediate deposition temperatures (1600-1700°C) the dominant morphology consisted of yellow prismatic crystals heavily twinned along {111} and {111¯}. At temperatures of about 1750°C hexagonally shaped {111}-oriented 3C-SiC platelets were formed with alternating {001}/{101} edges. A layer-by-layer growth model was used to rationalise the transition in preferred growth direction from 〈111〉 to 〈101〉 with increasing substrate temperature. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 10 (1966), S. 1121-1132 
    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: Reduced melting point and swelling measurements, involving heptane-soluble material from atactic polypropylene and over thirty liquids of differing chemical type, are reported. A value of 578 ± 40 cal. is obtained for the molar heat of fusion of a crystalline repeat unit which is much lower than values given for isotactic polypropylene. Some reasons for the low value are considered. Values of the polymer-solvent interaction parameter χ1 for systems involving alkylbenzenes and n-alkanes suggest a solubility parameter of 7.9 ± 0.1 (cal./cc)1/2 for the polymer. These values of χ1 decrease with increasing molar volume of liquid. Polar liquids of comparable solubility parameter or molar volume are associated with higher values of χ1. Intrinsic viscosities and values of the slope constant k′ are given for fractions in the molecular weight range 3,000-25,000 and six solvents at 25°C. The results suggest the following order of solvent power: cyclohexane ≈ cyclohexene 〉 methylcyclohexane 〉 trichloroethylene 〉 decalin 〉 carbon tetrachloride. Intrinsic viscosities are higher than those generally obtained for flexible polymers of comparable molecular weight, and the values of the Mark-Houwink exponent appear to be high. Some reasons for these high values are considered.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 8 (1964), S. 2619-2630 
    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: Osmotic, viscometric, and initial phase separation studies of dilute solutions of poly-(vinyl chloride) in cyclohexanone, cyclopentanone, tetrahydrofuran, morpholine, nitrobenzene, and tetrahydropyran are reported together with some swelling measurements involving these solvents and dioxane, acetone, and methanol. Values of the polymer-solvent interaction parameter χ1 obtained from osmotic and swelling measurements suggest the order of solvent power for poly(vinyl chloride) to be cyclohexanone 〉 cyclopentanone 〉 tetrahydrofuran 〉 morpholine 〉 nitrobenzene 〉 tetrahydropyran. A similar order is suggested by the volumes of hexane required to cause initial phase separation. Values of intrinsic viscosity and of the viscosity slope constant k′ give somewhat different orders of solvent power. Reasons for differences in order are considered. The correlation of the volume of hexane required to cause initial phase separation with χ1 is discussed and it is suggested that the polymer is solvated in solution. Other factors affecting the solvent power of solvents for poly(vinyl chloride) would appear to include the bulk and the solubility parameter of the solvent.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 15 (1955), S. 305-319 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Absorption of solvent and swelling by nitrocellulose fibers and films, in binary solventhexane mixtures of varying concentration and involving ketones, acetates, and phthalates, have been compared. Equilibrium is less rapidly attained with films. With solvents of smaller molecular size the equilibrium absorption of fibers and films, at a given concentration, is the same, suggesting that all regions of the nitrocellulose are accessible to such solvents. With solvents of larger molecular size lower equilibrium absorption values are obtained with films, suggesting that only certain regions are accessible to these solvents and such accessibility is less in films. Where absorption values are similar, swelling of films and fibers are comparable and similar modes of solution are observed. The assumption that no hexane is absorbed appears to be justified at lower solvent concentrations, but at higher concentrations the mixture in equilibrium with the nitrocellulose may be imbibed. Assuming such imbibition, the relationship between swelling or solvent power and cohesive energy density of solvent is interpreted in terms of interaction between solvated polymer and mixture.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 29 (1958), S. 37-52 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Heats and entropies of dilution of dilute solutions (concentration range 0.2-1.0 g./100 ml.) of cellulose acetate, ethyl cellulose, and cellulose nitrate, of similar degrees of substitution and polymerization, in a number of representative solvents, have been obtained from temperature coefficients of osmotic pressure. In some cases, degradation of polymer at the higher temperature used seems possible and an attempt is made to allow for this in the estimation of values of ΔH̄1 and ΔS̄1. Heats of dilution for the cellulose acetate and ethyl cellulose systems are generally endothermal, those for the cellulose nitrate systems being exothermal. Entropies of dilution are less than those obtained for comparable systems containing less polar and more flexible polymers. Those for the cellulose nitrate systems do not differ much from “ideal” values. The value of ΔH̄1/φ22, where φ2 is the volume fraction of polymer calculated from the density of the bare polymer, for each cellulose acetate system and most of the ethyl cellulose systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems become less negative as the concentration increases. Values of ΔH̄1 for the cellulose acetate and ethyl cellulose systems are generally in the order to be expected from the solubility parameters of the solvents and polymers. ΔS̄1/φ22 may vary with concentration in a manner rather similar to that suggested by simpler lattice theories. These results are tentatively interpreted in terms of solvation of polymer and possible endothermal mixing of solvated polymer and solvent. Although values of the entropy contribution to the interaction parameter χ1 for the cellulose acetate and ethyl cellulose systems are not always inagreement with the predictions of simpler lattice theories it is possible, if solvation, segment size, and chain stiffness are allowed for, that the thermodynamic properties of dilute solutions of cellulose derivatives may be at least qualitatively interpreted in terms of such theories.
    Additional Material: 4 Ill.
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