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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 19 (1981), S. 1721-1732 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This investigation deals with the nature and relative abundance of stable radicals formed by gamma-irradiation of wheat starch at room temperature. Additions of equal weights of water, methanol, and ethanol were equally effective in reducing the content of stable radicals in starch which contained about 12% water before the additions. When, however, the starting material was dried starch with 2.9% initial water content additional water and methanol were better radical scavengers than ethanol. This difference is attributed to the superior ability of water and methanol to permeate the starch structure. Superficially different ESR spectra were obtained in products made by irradiating starch and starch that contained added water or methanol. Computer simulation of these spectra showed that they could be matched by superposition of the spectra of the same four component radicals, with some adjustments of relative intensities and peak widths. The structures of these radicals have been dedueed from the spectral assignments and relative effects of the three solvents used on the intensities of the respective ESR spectra.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 19 (1981), S. 1707-1719 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starch-g-polystyrene copolymers were made by simultaneous 60Co irradiation of mixtures of wheat starch and styrene at room temperature. The extent of conversion of monomer to polymer is increased drastically with increasing water content up to a level of about 26 wt % on starch. Methanol had approximately the same effect as water at equivalent concentrations but ethanol was clearly less effective as a promoter of homo- and graft copolymerizations. Drying the starch reduced the conversion to polymer with all promoters but caused the greatest deterioration in the ability of ethanol to promote polymerization. The effects of physically swelling the starch by freeze drying the gelatinized material were also studied, as were preirradiation graft copolymerizations. The effects of promoters on graft polymerization parallel their abilities to scavenge stable radicals in irradiated starch. Water and methanol are better radical scavengers and polymerization promoters because they are better able to disrupt hydrogen bonds and permeate the starch structure. Radiolysis of the promoter is important in the grafting reaction.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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