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  • Polymer and Materials Science  (59)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 134 (1985), S. 63-71 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Einige Aspekte des viskoelastischen Verhaltens von 10 Blends von Polypropylen und langverzweigtem Polyethylen wurden untersucht. Messungen der Scherviskosität sind bei Temperaturen von 180-220°C und bei Scherraten von 1 - 1 000 s-1 durchgeführt worden. Die Elastizität wurde in Form der Strangaufweitung, des Anfangsdruckverlustes und der Schrumpfeffekte untersucht. Die auffallendsten Ergebnisse sind die enormen Schrumpfeffekte, die an Extrudaten bei 180°C beobachtet wurden; für einige Blendzusammensetzungen erreicht die Abnahme der Anfangslänge der Probe einen Wert von 800%.
    Notes: Some aspects of the viscoelastic behaviour of 10 blends of polypropylene and long branched polyethylene have been studied. Shear viscosity measurements have been carried out at temperatures from 180 to 220°C and shear rates from 1 s-1 to 1 000 s-1. The elasticity has been studied in terms of the extrudate swell, entrance pressure losses, and shrinkage effects. The most striking results are the enormous shrinkage effects observed on the extrudates at 180°C: for some blend compositions the reduction of the initial length of the sample attains a value of 800%.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 963-973 
    ISSN: 0887-6266
    Keywords: poly(ethylene terephthalate) ; crystal modulus ; mechanical properties ; force-field parametrization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A force-field suitable for the calculation of the mechanical properties of poly(ethylene terephthalate) and their relation with the molecular structure of the polymer has been developed. The force-field parameters were derived from quantum mechanical AM1 calculations and tested against thermodynamic and vibrational spectroscopy data available for a set of closely related small molecules. The crystal moduli of the two solid phases known for poly(ethylene terephthalate) were estimated by means of this new force-field considering both the isolated chain and the chain within the unit cell. Results were qualitatively consistent with reported x-ray data showing that the triclinic crystal form is stiffer than the mesomorphic phase provided that sample heterogeneities were taken into account. Although overestimated moduli resulted for both cases, divergences with experimental values were found to be slighter than those obtained by other theoretical methods. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 253-263 
    ISSN: 0887-6266
    Keywords: thermotropics ; dynamic viscoelasticity ; relaxation peaks ; gelation ; crystallization ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rheological characterization of two commercial thermotropic liquid crystalline polymers based on poly(ethylene terephthalate) (PET) and para-hydroxybenzoic acid (PHB) is carried out. The thermal transitions determined by DMTA are explained by the random character of these copolyesters, in comparison with non-random copolyesters synthesized by Jackson and Kuhfuss. The evolution of the dynamic viscoelastic functions with time in the nematic state is concave in shape for the 20%PET/80%PHB copolymer, a result that leads us to treat this system as a suspension of solid spheres (unmolten crystals) where the volume fraction of crystals increases with time according to an Avrami equation. The response of 40%PET/60%PHB copolymer is similar to a chemical or physical gelation and the hypothesis that the polydomain structure gives rise to a network is considered. Continuous flow, time-independent viscosity results reveal the existence of a three-region flow curve for 40%PET/60%PHB copolymer, but a Newtonian zone followed by a shear thinning region for 20%PET/80%PHB sample. At high temperatures the isotropization of the samples leads to a very strong decrease of the activation energy of flow, which becomes zero for 40%PET/60%PHB. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 253-263, 1998
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 18 (1997), S. 591-599 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extrusion rheometry experiments with a commercial thermotropic liquid crystalline copolyester show concave Bagley plots and convex pressure profiles. A loss of the orientation produced at the entrance of the capillary and the slit can explain these non-linearities. Assuming that the order parameter, S, relaxes exponentially with time, the Doi-Edwards model for the shear flow of rod-like polymers is used to adjust experimental data.
    Additional Material: 6 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
    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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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electroanalysis 5 (1993), S. 325-331 
    ISSN: 1040-0397
    Keywords: Cephalosporin ; Cefamycin ; Reduction ; Voltammetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical reduction at a mercury electrode of three cephalosporins and one cefamycin bearing a common R3 substituent was studied. The first one-electron transfer of the reduction process was found to be the rate-determining step in all four cases. In addition, the process took place via species adsorbed on the electrode. The analysis of the voltammetric peaks obtained in the absence of diffusion allowed us to establish the variation of the apparent transfer coefficient, αap, throughout the peak. This was found to be a linear function of the faradic current, which is consistent with the assumption that the free energy of adsorption of the antibiotics is a linear function of the coverage. In addition, the transfer coefficient was found to be markedly dependent on the nature of substituent R-and on the character of the cephalosporin or cefamycin.
    Additional Material: 7 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 10 (1989), S. 13-17 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 7 (1986), S. 553-555 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Tab.
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