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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 5251-5256 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    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.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 423-427 
    ISSN: 1042-7147
    Keywords: Liquid crystalline polymers ; Blends ; Viscosity reduction ; Reinforcing action ; Microfibrillar morphology ; 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
    Notes: Blends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 43-48 
    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: A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280°C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range 10-1 s-1 to 102s-1. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of liquid crystal, is more pronounced at high shear rates.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 307-311 
    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 industrial polymer processing, polymeric melts give rise to shear stresses above 105 dynes/cm2. For the determination of rheological properties and particularly melt elasticity, only the capillary type instrument is applicable to this range. In this paper, a comparative experimental study of the first normal stress difference, obtained from end pressure losses, entrance pressure losses and die swell is reported for polystyrene and high impact polystyrene. Good agreement between results from the three methods of measurement was obtained. The results are in accordance with literature data obtained using a capillary rheometer. It is seen that the values of first normal stress difference are greater in polystyrene than in high impact polystyrene.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 347-356 
    ISSN: 0887-6266
    Keywords: viscosity of melts by capillary and slit die methods ; liquid crystal polymers, viscosities, comparison of capillary and slit die result for ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Viscosity measurements on two commercial thermotropic liquid crystalline polymers (LCPs) (a copolyester and a polyesteramide) were performed using both capillary and slit die methods. The results are in agreement with those presented in the literature for the same LCPs, when the measurements are carried out with a L/D = 30 die; these results are affected more by Bagley corrections for the polyesteramide than for the copolyester. For both LCPs, viscosities measured in the slit die are lower than those obtained by capillary rheometry. Nevertheless, the difference is much bigger in the case of the polyesteramide, for which a reduction by a factor of 3 is observed. This is not due to the preshear or thermal history, since the same piston-barrel system and thermal treatment were applied in both types of measurements. Depending on the polymer sample and temperature, concave and convex curvatures were observed in the pressure profiles during the slit flow. From these curvatures, the pressure coefficient α of viscosity was evaluated. However, in the case of the polyesteramide the convex curvature leads to a negative coefficient (the viscosity decreases with pressure, instead of increasing). This result may be explained by envisaging a change in the structure of the melt along the slit length. © 1993 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 1129-1136 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The flow properties of concentrated solutions of polyarylate from bisphenol A/50:50 isophthalic acid: terephthalic acid in m-cresol are studied. The results are discussed in terms of critical concentration Cc and critical molecular weight Mc for the onset of entanglements. Values of Cc = 8,2 wt.-% and Mc ≈ 3500 are obtained. The dependence of the Newtonian viscosities with temperature allows to obtain different energies of activation of flow for each polyarylate/m-cresol system, ranging from 9 to 13 kcal/mol (= 37,7 to 54,4 kJ/mol). The following free-volume-additivity equation is proposed to fit these data: \documentclass{article}\pagestyle{empty}\begin{document}$ E_{\rm a} = \frac{{V_{\rm p} \cdot \alpha _{\rm p} \cdot E_{{\rm ap}} + V_{\rm d} \cdot \alpha _{\rm d} \cdot E_{{\rm ad}} }}{{V_{\rm p} \cdot \alpha _{\rm p} + V_{\rm d} \cdot \alpha _{\rm d} }} $\end{document} where Ea, Eap, and Ead are the activation energies of the solution, the polymer and the solvent, respectively. Vp and Vd are the polymer volume fraction and the diluent volume fraction, respectively, and αp and αd represent the differences between the volume coefficients of expansion above and below the corresponding glass transition temperatures for the polymer and the solvent.
    Additional Material: 5 Ill.
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  • 8
    Publication Date: 1990-12-01
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
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