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  • 1
    Electronic Resource
    Electronic Resource
    On the resistance to the interpenetration between macromolecular coils of different segment densities (1996)
    Springer
    Colloid & polymer science 274 (1996), S. 634-639 
    Details
    ISSN: 1435-1536
    Keywords: Binary polymer mixtures ; dilute solutions ; semi dilute solutions ; overlap concentrationc *
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using viscometry techniques on polymer fractions, we determine the critical concentrationc * (separating the dilute and semi dilute solutions). The same measurements have been conducted with mixtures of these fractions (mixtures 1:1 by weight of fractions differing in molecular mass and chemical nature, or fractions differing only in molecular mass). The determined values of critical concentrationc * of the mixtures are higher than the values calculated based on the critical concentrations of the corresponding fractions. This deviation from the additivity rule is attributed to the resistance in the interpenetration (delay to the attainment of the homogeneous state) between macromolecular coils of different chemical nature or of the same chemical nature but of different molecular mass. Higher values of the reduced viscosities of the mixture of the fractions, compared to the values calculated using the reduced viscosities of the corresponding fractions, are observed above the critical concentrationc *. In this concentration region the interaction parameter between two different polymers is calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00653060
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  • 2
    Electronic Resource
    Electronic Resource
    The influence of shear rate, temperature and chain conformation on the critical concentration c ** (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 709-715 
    Details
    ISSN: 1435-1536
    Keywords: Key words Extremely dilute solutions ; critical concentration c** ; chain entanglements ; solution shear rate ; viscometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  When viscometry is used, a crossover phenomenon is observed separating the dilute solutions into extremely dilute solutions and dilute solutions. The critical concentration c **, determined from this crossover phenomenon, strongly depends on the shear rate in the solution. At very high values of shear rate the critical concentration c ** becomes very low and depends only on the contour length of the elongated chains of different polymers. An increase of the temperature induces an increase of c ** because the relaxation time of the chains decreases. If a polymer adopts a rodlike conformation (in a given solvent at a given temperature) the excluded volume of its chains increases and its critical concentration c ** decreases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050139
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Towards a better mixing of two incompatible polymers by casting from solution without compatibilizer (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1051-1060 
    Details
    ISSN: 0887-6266
    Keywords: polymer mixtures ; film casting ; solvent selectivity ; incompatibility ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Blends of polystyrene/poly(oxyethylene) (PS/POE) and polystyrene/poly-(methyl methacrylate) (PS/PMMA) have been obtained by casting from solution. Differential Scanning Calorimetry, Optical Microscopy, and Scanning Electron Microscopy showed that two incompatible polymers can present relatively good miscibility (formation of domains smaller than 5 μm) when the solvent from which the films are obtained does not present any noticeable selectivity towards the two polymers of the blends. An increase of the casting temperature increases the miscibility of PS and PMMA because the selectivity of the solvent used, towards these polymers decreases with increasing temperature. On the contrary, an increase of the casting temperature in the case of the PS and POE mixture decreases their miscibility because the selectivity of the solvent used increases with increasing temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1051-1060, 1998
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    New developments in synthesis of star polymers with poly(ethylene oxide) arms (1993)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 44 (1993), S. 225-229 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis of star molecules consisting of small polydivinylbenzene (DVB) cores carrying a number of hydrophilic poly(ethylene oxide) branches has been investigated. Two different methods are discussed:The “core-first” technique, in which living poly(DVB) cores are used to initiate the polymerization of oxirane. This method is flexible and efficient, but the samples obtained exhibit broad molecular weight distributions, arising from large fluctuations of the core functionalities (and core sizes). The same method has been applied successfully to the synthesis of star-block copolymers, in which each branch consists of a polystyrene (PS) block and a poly(ethylene oxide) (PEO) block.The “three-step” method (“In-Out”) involves the use of living polystyrene “seed-star” molecules as initiators for the polymerization of oxirane. The “seed-stars” themselves arise from a classical “arm-first” process. This method allows a better control of the functionality of the cores. The number of branches of either kind attached to a given core is equal. Hetero-star PS-PEO copolymers are obtained, but the length of the branches of either kind can be chosen at will within broad limits.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1993.010440503
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    Paper (German National Licenses)
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