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  • Articles  (33)
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  • Polymer and Materials Science  (28)
  • Chemical Engineering  (4)
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  • Surface physics, nanoscale physics, low-dimensional systems
  • 1990-1994  (33)
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  • Articles  (33)
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  • 1
    Electronic Resource
    Electronic Resource
    Non-Newtonian and isothermal analysis of flow of poly(methyl methacrylate) in a model twin screw extruder. Part I (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 986-994 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 flow analysis network (FAN) method was modified to analyze the flow of poly(methyl methacrylate) (PMMA) in a model counter-rotating nonintermeshing screw extruder. The numerical prediction of the pressure profiles was compared with the experimental results. Flow patterns in the screw elements of the model counter-rotating nonintermeshing twin screw extruder were also predicted. A new flow path method was developed to calculate the residence time distribution. This result will be applied to analyze the flow during the reaction in the model twin screw extruder.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760341207
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear wave theory for dynamics of binary distillation columns (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 705-723 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A major difficulty in control of distillation columns stems from their nonlinear behavior, especially of columns producing high-purity products. Based on a previous development that adapted fixed-bed theories to simple countercurrent processes, this study has established a nonlinear wave theory for the nonlinear and distributed dynamics of binary distillation columns by including the effects of reflux, reboil, and combination of sections. This theory clearly elucidates the intriguing dynamic behavior of distillation columns such as high steady-state gains, large response lags, strong dependence of dynamics on the magnitudes and directions of disturbances, and asymmetric dynamics of the transitions between two steady states. It also underlines the inadequacy of conventional linearized models for high-purity columns. With fairly simple mathematics, this nonlinear wave approach may be useful for model development, control system design, dual-composition control, and feedforward control.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370509
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  • 7
    Electronic Resource
    Electronic Resource
    The thermal deprotection process in an e-beam exposed phenolic-based polymer (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1589-1594 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: In our current work, we have examined the e-beam sensitivity and thermal processing behavior of pure PBOCST [poly(tert-butoxycarbonyloxystyrene)]. An alkali soluble latent image can be generated in the PBOCST by e-beam exposure followed by a post-exposure bake (PEB) at relatively high temperatures (140 to 150°C). Pattern wet development operates on the same basis as a PBOCST/acid generator two component system. Deprotection, accelerated by the exposure, yields alkali soluble areas, while unexposed areas remain insoluble. Sensitivities of 5 to 10°C/cm2 and contrasts of 6 to 10 have been measured. Complete TBOC deprotection results in a film thickness loss of 35 to 40% as CO2 and isobutene are evolved. A laser interferometer/hotplate setup was used to track film thickness with time during the thermal deprotection process. IR analysis confirmed the correlation between conversion and thickness. It was found that a slow initial conversion rate was followed an exponentially steep rise in rate after 50% conversion. Activation energies were on the order of 30 kcal/mol. It was concluded that thermolysis in both exposed and unexposed resist occurred during the PEB, but that the difference in extent of conversion on exposure was sufficient to generate a pattern.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760322108
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  • 8
    Electronic Resource
    Electronic Resource
    Non-Newtonian and non-isothermal analysis of flow during polymerization of methyl methacrylate in a model twin screw extruder. Part II (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 995-1004 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 flow analysis network (FAN) method was modified to analyze the flow during polymerization of methyl methacrylate (MMA) in a model counter-rotating nonintermeshing screw extruder. The shear viscosity of the reactive mixture in the twin screw extruder was considered as a mixture of polymer and monomer. Thus, the reaction viscosity of the mixture of polymer and monomer was taken to be an explicit function dependent on the shear rate, temperature, conversion, and molecular weight. A new flow path method was developed to calculate the residence time distribution, which related to the degree of conversion. The numerical prediction of the velocity, temperature, viscosity, and pressure profiles during reaction in the model twin screw extruder is described.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760341208
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  • 9
    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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  • 10
    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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