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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 731-744 
    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 new mathematical model has been derived for a semicontinuous recycle esterification process that consists of two reactors, one has the recycle flow to or from another and the discharge flow of the main flow and another has only recycle flow without the discharge flow. This model can give useful information about the optimum design of a new plant through the predictions of oligomer characteristics such as concentrations of carboxyl and hydroxyl end groups, number-average molecular weight, number-average degree of polymerization, esterification and saponification degree, diethylene glycol content, melting point, concentrations of ethylene glycol and water in the vapor phase, and so on.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 765-781 
    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: Experiments at various concentrations for A and B kinds of titanium dioxide were made in the pilot plant, and the effect of titanium dioxide on continuous esterification between terephthalic acid and ethylene glycol was obtained. Reaction rate constants of the reaction scheme reported by Yamada et al. (1985) were determined o fit with the experimental data obtained. It was found that titanium dioxide ([TDO]) does not exert an influence on the reaction rate constants of k1, k2, and k4 but does on the reaction rate constants of k3, k5, k6, and k7 as follows: kl = 1.5657 × 109 exp(-19,640/RT)k2 = 1.5515 × 108exp(-18,140/RT)k3 = (0.10[TDO] + 1) × 3.5165 × 109 exp(-22,310/RT)k4 = 6.7640 × 107 exp(-18,380/RT)k5 = (0.08[TDO] + 1) × 7.7069 exp(-2,810/RT)k6 = (0.04[TDO] + 1 ) × 6.2595 × 106 exp(-14,960/RT)k7 = (0.60[TDO] + 1) × 2.0583 × 1015 exp(-42,520/RT) for B kindk7 = (0.085714[TDO] + 1) × 2.0583 × 1015 exp(-42,520/RT) for A kind Applying these reaction rate constants, simulation of continuous esterification in the first tank reactor was made and the following results were obtained ( 1) The acceleration effect of titanium dioxide on the esterification reaction is minor, and there is hardly any difference in the effect on the esterification due to kinds of titanium dioxide. ( 2 ) The amount of diethylene glycol formation largely varies with kinds of titanium dioxide.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have recently undertaken a systematic structural analysis of fully protected tetrapeptides containing at the N- and C-terminus either homo- or heterochiral amino acids, spaced by an achiral dipeptide segment. The interest for this class of peptides derives from the observation that, on reverse-phase (HPLC), the homo- and heterochiral sequences have a markedly different retention times. The diastereomeric sequences, namely Z-(L/D)-Val-X-Y-L-Phe-OMe (X = Sar, Gly, Ac3c, Aib, Ac5c, Ac6c, Deg, Dpg, Dbu, Dip, Dph; Y = Sar, Gly, Ac3c, Aib, Ac6c, Ac6c) show different overall hydrophobicity attributed to a different three-dimensional structure that also depends on the X-Y segment. Therefore, following preliminary studies in solution, we report here the detailed x-ray analysis of the tetrapeptide Z-D-Val-Ac6c-Gly-L-Phe-OMe in order to understand the structural features governing the overall hydrophobicity of linear fully protected tetrapeptides. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report here the synthesis and molecular structure in the solid state of fully protected tripeptides containing Cα,α-diphenylglycine (Dph), namely Z-Aib-Dph-Gly-OMe (Aib: Cα,α-dimethylgrycine) and Bz-Dph-Dph-Gly-OMe. The molecular conformation around the Dph residue, containing two bulky substituents, is fully extended, while the Aib residue, containing two smaller groups on the Cα atom, adopts the typical 310/α-helical conformation. Gly residues, without substituents on the Cα atom, show different conformational preferences. Each residue seems to behave, from a conformational point of view, independently from the presence of the other residues, and thus mixed local conformations (folded and extended) are present in the crystals. The nonconventional peptide synthesis, using the Ugi reaction, is also reported. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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