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  • 1
    Electronic Resource
    Electronic Resource
    Conformational changes of amorphous poly(ethylene terephthalate) films during uniaxial stretching (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 301-307 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rapid scanning Fourier transform infra-red spectroscopy was used to follow the changes in the population of trans conformers and in the infra-red dichroic functions of the bands characterizing the trans (T) and gauche (G) conformers and the chains in the amorphous regions during stretching of a solution-cast amorphous poly(ethylene terephthalate) (PET) film A in the glassy state (67°C) and in the rubbery state (88°C). Stretching at 67°C showed a yield stress peak followed by strain softening in the stress-strain curve. The population of trans conformers in the amorphous and crystalline regions, Ta + Tc, decreased in the pre-yielding region and then increased continuously after yielding. The T conformers formed during post-yield stretching showed high orientation, while the G conformers remained in low degree of orientation. Stretching at 88°C showed no pronounced yield stress peak in the stress-strain curve, and the population of T conformers did not change until the beginning strain-induced crystallization. A solvent-cast PET film annealed at 67°C for 24 h, the film N, showed a sharp and high yield stress peak in the stress-strain curve, and strain-induced crystallization occurred at lower draw ratio as compared to the film A. The film A showed a non-equilibrium high population of Ta conformers, part of which reverted to G conformers during sub-Tg annealing.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920212
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  • 2
    Electronic Resource
    Electronic Resource
    Epoxy modified polyurethane rigid foams (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1083-1088 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rigid IPN foams were prepared by sequential polymerization of polyurethane and epoxy systems. Significantly higher compressive modulus and strength were observed with the IPN foams in comparison to the corresponding polyurethane rigid foams. The IPN foams show one glass transition temperature. The single Tg indicates the very small domain size in the PU-epoxy IPN's.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290801
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  • 3
    Electronic Resource
    Electronic Resource
    Thermogravimetric analysis of poly(alkyl methacrylates) and poly(methylmethacrylate-g-dimethyl siloxane) graft copolymers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1747-1753 
    Details
    ISSN: 0887-624X
    Keywords: poly(methyl methacrylate) ; polydimethylsiloxane ; thermogravimetric analysis (TGA) ; graft copolymers ; poly(alkyl methacrylates) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal stabilities of various poly(alkyl methacrylate) homopolymers and poly(methyl methacrylate-g-dimethyl siloxane) (PMMA-g-PSX) graft copolymers have been determined by thermogravimetric analysis (TGA). As expected, the thermal stabilities of poly(alkyl methacrylates) were a function of the ester alkyl group, and polymerization mechanism. In particular, thermally labile linkages, which result from termination during free radical or nonliving polymerization mechanisms, decrease the ultimate thermal stabilities of the polymers. However, graft copolymers, which were prepared by the macromonomer technique with free radical initiators, exhibited enhanced thermal stability compared to homopolymer controls. A more complex free radical polymerization mechanism for the macromonomer modified polymerization may account for this result. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320917
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  • 4
    Electronic Resource
    Electronic Resource
    Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2425-2430 
    Details
    ISSN: 0887-624X
    Keywords: anionic ; polymerization ; living ; methyl methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at -78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (〈1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO4. Number-average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (〉2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent-separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321303
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  • 5
    Electronic Resource
    Electronic Resource
    NMR and CD studies of triple-helical peptides (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 447-451 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Triple-helix formation of the peptide (Pro-Hyp-Gly)10 was monitored by nmr and CD spectroscopy. The two-dimensional nmr spectra indicated that the Gly Cα H and Pro CδH proton resonances shift upfield in going from the nonhelical to helical form, while hydroxyproline resonances are unchanged. The integrated areas of the helical and nonhelical resonances could be monitored in the one-dimensional nmr spectrum, and indicate that in the (Pro-Hyp-Gly)10 about 90% of the residues are in a defined triple-helical conformation. The introduction of a glycine to alanine substitution or the deletion of a single hydroxyproline residue in the stable triple-helical peptide (Pro-Hyp-Gly)10 still allows trimers to be formed, but the trimers show a substantial loss of triple helix and decreased thermal stability compared with (Pro-Hyp-Gly)10. Two computer models were generated for the Gly → Ala peptide, one with the Ala side chains packed inside the helix and the other with the region containing the alanines forming a β-bend that loops out from the helix. The nmr data is more consistent with the latter model.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320423
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement of long-range2 13C-1H coupling constants of 95% uniformly 13C-labeled polysaccharide from streptococcus mitis J22 (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1327-1338 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coaggregation of Streptococcus mitis strain J22 in the early stages of dental plaque formation has been shown to result from interaction of cell wall polysaccharides with lectins on the surface of other oral bacterial species. This bacterium was grown in a medium containing 13C as the sole carbon source. We have isolated the lectin receptor polysaccharide from this strain with full enrichment in 13C and have determined a number of two-bond and three-bond 13C-1H coupling constants from measurements of the offsets in two-dimensional homonuclear nmr spectra [exclusive correlated spectroscopy (E-COSY) method]. A scheme for reliable extraction of these coupling constants from homonuclear Hartmann-Hahn and nuclear Overhauser effect spectroscopy spectra is tested in model compounds. We interpret the three-bond coupling across the glycosidic linkage in terms of dihedral angles in order to provide conformational information to supplement molecular modeling and nuclear Overhauser effect data. We show that the E-COSY method works well even for coupling constants smaller than the nmr line width and that a number of the 3JCH across the glycosidic linkage are in the range of 1-2 Hz, which is much smaller than many previously reported values. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341005
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  • 7
    Electronic Resource
    Electronic Resource
    Percolation effects in degradable polyethylene-starch blends (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 565-579 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The accessibility of starch in polyethylene starch blends was investigated by computer simulation, percolation theory, and acid hydrolysis experiments. The object of this work was to model the bilateral invasion of microbes in polyethylene-starch blends as a function of starch concentration (p), and thickness of the material. It was found that computer simulations in three dimensions were in agreement with both percolation theory and the acid digestion experiments. In computer simulation the accessibility is highly dependent on the percolation threshold concentration (pc), which is 31.17%. Similarly, the accessibility of starch is highly dependent on an apparent percolation threshold near 30% by volume or approximately 40% by weight of starch. At p 〈 pc a small amount of starch is removed from the surfaces only, but at p 〉 pc connected pathways existing throughout the bulk of the material facilitate large amounts of starch extraction. The sharpness of the transition at pc increases with the ratio of sample thickness to starch particle size. The results of this work have application to conduction and reacting systems where one component is dispersed in a matrix of the other.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1991.090290506
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  • 8
    Electronic Resource
    Electronic Resource
    General procedures to determine the composition of commercial, two-part polysulfide aircraft sealants (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 41 (1990), S. 2837-2856 
    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: Interpretation of the chemical processes which polysulfide sealants undergo either on storage or when the cured material is subjected to environmental influences requires detailed knowledge of formulations. Procedures have been developed to isolate and identify a range of additives in two-part commercial aircraft sealants of both the dichromate and manganese dioxide cure types. Solvents, curing agent dispersants, and cure rate modifiers were separated chemically and thermal analysis was demonstrated to provide a ready means to estimate carbon in fillers. The phenolic resin adhesion enhancers were conveniently determined using 13C-NMR spectroscopy and could also be identified using size exclusion chromatography. It was shown that virtually no interaction occurred between polysulfide liquid polymers and phenolic resins following aging at 70°C for 7 days. The most appropriate methods for determining curative levels were established and new means of assessing thiol content of the polysulfides by both 13C-NMR and PMR spectroscopy are described. The significance of aspects of the sealant formulations is discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1990.070411126
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  • 9
    Electronic Resource
    Electronic Resource
    Shrinkage force studies of oriented polyethylene terephthalate (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 1921-1929 
    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: Shrinkage force measurements on drawn polyethylene terephthalate fibres have been evaluated in terms of the elastic behaviour of a molecular network. It is shown that for low network deformations the classical theory of Kuhn and Grün describes the stress-optical behaviour very well. For high deformations, the recent theory of Edwards and Vilgis has been found to give a satisfactory description of the data. It also provides some tentative insights into the structure of the spun yarns.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070420715
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  • 10
    Electronic Resource
    Electronic Resource
    Structural changes on plasma irradiation of ethyl-cyanethyl cellulose as revealed by infrared spectroscopic technique (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 19-22 
    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: Ethyl-cyanethyl cellulose was treated with oxygen plasma using the RF glow discharge technique. Three different plasma-treated samples, including gel fraction, soluble fraction, and newly polymerized product by small moleculars given off by ethyl-cyanethyl cellulose, were obtained. With the infrared spectroscopic technique, the structural differences caused by plasma were studied. The effect of different gas plasma N2, Ar, and O2 on the structure of ethyl-cyanethyl cellulose was also studied.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070430103
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