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  • Wiley-Blackwell  (16)
  • Springer Nature  (2)
  • 2000-2004
  • 1995-1999  (18)
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  • 1995  (18)
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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 299-305 
    ISSN: 0887-624X
    Keywords: polygluconamides ; stereoregular polyamides ; stereoregular nylons ; chiral polyamides ; chiral nylons ; aminoaldonic acids ; sugar polyamides ; carbohydrate monomers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two stereoregular polygluconamides, one (3) of polypeptide-type and the other (16) being a polycaproamide containing four stereocenters in the main chain of the repeating unit, have been prepared from D-glucosamine and D-glucose, respectively. The new polyamides were characterized by elemental analysis, and IR, 1H- and 13C-NMR spectroscopies. The molecular weights for 3 and 16 were estimated as 25,000 and 67,000, respectively, on the basis of viscosimetric measurements. Both polyamides display high optical activity; they are highly hydrophilic and readily soluble in water as well as in a variety of organic solvents including chloroform. Polyamide 16 is highly crystalline and yields resistant films with spherulitic texture. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2300-2305 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relative merits of various approaches using computer simulation methods for estimating first-order correction terms to Henry's law in dilute supercritical mixtures are investigated. Three thermodynamic formulations are provided for the calculation of these properties. One method, termed the fluctuation integral approach, requires the explicit calculation of solute-solvent pair correlation functions at the infinite dilution limit, which is a difficult task for simulations given the conflicting demands of both small numbers of solute species (for approximating the infinite dilution limit) as well as the need for large numbers of solute species to improve simulation statistics. A second approach, called the pressure gradient method, does not require the explicit, determination of these solute-solute functions and, as a result, is not as sensitive to the choice of system size and other difficulties associated with establishing an adequate ensemble size and/or number of solute species to be used in the simulations. The third approach uses the exact formulation for the property of interest using Kirkwood-Buff theory. This approach, however, requires all the solute pair correlation functions to be established, making it the most sensitive to issues concerning number of solute species used in the simulations, and so on. An examples is given showing simulation results for these approaches, illustrating their respective strengths and drawbacks.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 389-401 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An asymptotic analysis based on Taylor series expansions is used for first-order correction terms to the Henry's law approximation to describe solvation phenomena in multiple solute-multiple solvent systems. The magnitude of these correction terms in solvent systems very near their critical points is of particular concern, as shown in model fluid calculations with the aid of integral equation theory. The results clearly demonstrate that close proximity to the critical point in pure and mixed solvent systems causes the Henry's law approximation to show large errors in predicting solubilities, especially near the critical azeotrope of a mixed solvent system. Theoretical results also show that cross solubility enhancements in a two solutesupercritical solvent system cause cooperative synergism (both solute solubilities are increased relative to the corresponding single solute situations) or reverse synergism (both depressed relative to the single solute situation). It appears to be consistent with the available data. In computer simulations, the solute's infinitely dilute reference state is often used as a basis for describing solute thermodynamic behavior. These simulations are best achieved in the canonical ensemble because of the weak composition dependence of free energies in terms of characteristic variables of this ensemble.
    Additional Material: 9 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 36 (1995), S. 263-271 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(β-l-aspartate)s are known to take up helical conformations reminiscent of the α-helix of polypeptides. The isobuttyl, n-butyl, and 2-methoxyethyl esters have been examined by polarized ir spectroscopy in order to discriminate between the left (1L) and right (2R) -handed conformations, which are known to be compatible with the 13/4-helix adopted by these polyamides when crystallized in the hexagonal form. Dichroic ratios obtained from samples stretched in poly(ethylene oxide) together with orientation measurements made by x-ray diffraction were used to estimate the transition moment directions of amide A, I, and II bands with respect to the fiber axis. These were compared to those calculated by modeling simulations to conclude that the right-handed conformation consisting of 14-membered hydrogen-bonded rings is the correct model for the 13/4-helix. These results give definite support to earlier molecular mechanics calculations, which had shown that the 2R model is energetically favored over the 1L by about 2. 5 kcal/(mol residue). © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 16 (1995), S. 417-424 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rheological and thermal analysis results of blends of a thermotropic copolyesteramide and polyarylate of bisphenol A depend on the thermo-mechanical treatment during mixing. The changes observed as mixing time increases are the following: (a) melt viscosity and loss factor increase, (b) glass transition temperature decreases. The morphological analysis of the blends shows the inability of the treated blends to form an oriented liquid crystalline polymer (LCP) phase, which explains the observed viscoelastic properties.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A structural study was carried out on poly(α-butyl β-L-aspartate), which is a stereoregular nylon-3 derivative with an alkoxycarbonyl group attached to the β-carbon of the main-chain repeating unit. Two crystal forms, namely hexagonal and tetragonal, made of 13/4 and 4/1 helices, respectively, and bearing a structural resemblance to the polypeptide α-helix, were characterized by X-ray diffraction. Though these forms are basically identical to those previously reported for poly(α-isobutyl β-L-aspartate), the crystal transition from hexagonal to tetragonal known to take place in this polymer by effect of heating, was not observed in the present case. Modeling calculations revealed that although similar conformations are favoured for the two polymers in both crystal forms, the relative stability of the 13/4 helix to the 4/1 helix was found to be significantly reduced in the case of the butyl derivative. The presence of helical conformation in solution has been evidenced by both 1H NMR and circular dichroism and the helix-coil transition promoted by acids was investigated by means of these techniques.
    Additional Material: 7 Ill.
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  • 7
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Preparative temperature rising elution fractionation (TREF) on commercial linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) samples has been performed. The resulting fractions exhibited a bimodal and a unimodal distribution, respectively. Two LLDPE fractions of low (5 CH3/1000 C) and high (21 CH3/1000 C) short-chain branching content were solution-mixed with the LDPE central fraction (16 CH3/1000 C). Indirect evidence based on differential scanning calorimetry results suggest that the fractions with similar branch contents are more miscible than those with dissimilar ones.
    Additional Material: 10 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 3133-3142 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We report dynamic viscoelastic measurements of a series of binary blends of hydroxyethyl ether of starch and ethylene-vinyl acetate copolymer (EVA), which are correlated with the granular arrangement of the starch derivative within the EVA matrix and the adhesion between both phases, studied by scanning electron microscopy. The rheological properties are similar to those of polymers filled with solid spheres, although we found a minimum in the Newtonian viscosity and a maximum in the elasticity at low starch derivative concentrations, which have been attributed to a change in the density of chain entanglements.
    Additional Material: 11 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 41-54 
    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: This article describes the hydrolytic degradation of a series of nylons based on methylated L-tartaric acid and diamines. These polytartaramides were prepared by a solution polycondensation process using bis(pentachlorophenyl)-2,3-O-dimethyl-L-tartrate and N,N′-bis(trimethylsilyl)alkanediamines with 6, 8, or 12 methylene groups. The stereoregular optically active polyamides obtained were soluble in chloroform and showed intrinsic viscosities between 1.0 and 2.7 dL g-1. The degradation of these polytartaramides in the form of discs has been investigated in buffered salt solutions of pH 2.3, 7.4, and 10.6, and at temperatures of 37, 55, and 70°C. The degradation was monitored by following the changes in molecular weight, mass loss, chemical constitution, and thermal properties. Our results show that these polytartaramides degrade slowly at 37°C, with a degradation rate highly depending upon the number of methylenes in the diamine unit of the polyamide. The pH of the medium has also a great influence on degradation, as well as the temperature, with an important hydrolysis rate enhancement at 70°C. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 559-562 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The monocation-dication equilibria of 6-nitro and 6-sulphonic acid derivatives of betacarboline (9H-pyrido[3,4-b]indole) were investigated mostly by UV-visible absorption spectroscopy. Dications are formed in very highly concentrated sulphuric acid solutions (〉15 M). Ionization constants, pKa values and solvation parameters obtained from the excess acidity method are reported. The unusually high m* parameters are discussed and compared with other related data.
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