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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 405-414 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In both thermal emulsion polymerization of styrene in the temperature range 60-80 °C, and peroxodisulfate-initiated polymerization at 60 °C, weight-average to number-average molecular-weight ratios (M̄w/M̄n) approach 1,5 when potassium octadecanoate is used as emulsifier. A low activation energy for thermal initiation (≈66,0 kJ/mol) was deduced which may indicate a catalytic effect of the emulsifier during the thermal initiation process. Participation of the emulsifier is probably attributed to a transfer of one of two monomer radicals, produced thermally, to the emulsifier, with subsequent desorption to the aqueous phase, leaving one radical in the polymerization locus.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 40 (1996), S. 307-313 
    ISSN: 0959-8103
    Keywords: swelling ; seed ; electrolyte ; particle size ; rate of polymerisation ; coalescence ; styrene ; 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: The effects of adding inorganic electrolyte (below the critical coagulation concentration) have been investigated in two systems for the emulsion polymerisation of styrene. In one system, potassium chloride, at different concentrations, was added at the end of interval I, using three different ionic emulsifiers: potassium octadecanoate which has a low critical micelle concentration (CMC), potassium dodecanoate and sodium dodecyl sulphate (SDS), which have moderately high CMC. A significant increase in the rate of polymerisation was observed in all cases even at the higher levels of electrolyte at which the rate is reduced if the electrolyte is added from the onset of polymerisation. In the second system, the effects of adding sodium chloride, in concentrations up to 0.2M, on the seeded emulsion polymerisation of styrene have been followed. A significant increase in the rate was observed as electrolyte level was increased, with no significant change in particle size. Saturation swelling measurements indicated a slight increase in monomer concentration inside the particles as electrolyte concentration was increased. Evaluation of the average number of free radicals per particle, n¯, by a steady state approach indicates an increase in the value of n¯ as electrolyte level is increased. The value of n¯ is below 0.5 but approaches this value at the highest electrolyte concentration. The increased surface area of the particles may account for this effect by increasing the capture efficiency of the radicals by the particles.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 35 (1994), S. 379-387 
    ISSN: 0959-8103
    Keywords: electrolyte ; latex ; particle size ; rate of polymerisation ; polydispersity ; adsorption ; 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: The effects of adding potassium chloride in concentrations below that required to coagulate the latex to recips of emulsion polymerisation of styrene have been investigated using different concentrations of potassium octadecanoate, which has a low critical micelle concentration (CMC), and potassium dodecanoate, which has a moderately high CMC. At relatively high concentration of octadecanoate the final particle size is significantly increased; the rate of polymerisation is initially increased but later retarded. The effects of increasing micelle size and increased rate of coalescence are dominant. At lower concentration of this emulsifier, the rate is reduced from the onset of interval II.With dodecanoate, concentrations of electrolyte up to 0.3 M accelerate the rate. No significant change in the particle size was observed up to 0.2M electrolyte, thereafter it slightly increased. The increase in micellar concentration can only partially account for these effects. It is believed that the increase in the amount of solubilised monomer inside the micelles, and later inside the latex particles, and the resistance to coalescence (because of the favourable adsorption mechanism of this emulsifier) may account for these observations.With both emulsifiers, electrolyte reduces the induction period and latices with narrow particle size distributions are produced.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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