ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The existence of trapped radicals in polymers prepared heterogeneously from vinyl monomers was first deduced from kinetic observations and subsequently confirmed by electron resonance spectroscopy. We have used this latter technique to determine the concentration of trapped polyacrylonitrile radicals obtained as a function of the experimental variables including the degree of swelling of the polymer, the rate of photo-initiation and the temperature of polymerization. In the bulk polymerization of acrylonitrile at 25°C. the fraction of radicals which become trapped is approximately 12% for a conversion of 17%. The concentration of trapped radicals obtained in the presence of N,N-dimethylformamide increases for low concentrations of the swelling agent, passes through a maximum, and subsequently decreases to zero. Qualitatively similar behavior is obtained if the swelling of the polymer is increased by the incorporation of methyl acrylate as commonomer. Addition of a swelling agent to the active photopolymer leads to destruction of the radicals. An increase in the concentration of trapped radicals with increasing light intensity (for a given conversion) is observed initially; at very high intensities the concentration decreases to zero. There is a marked decrease in the concentration of radical as the temperatur of polymerization increase; it is doubtful if trapping occurs significantly at 60°C. There observations are discussed in terms of previous kinetic studies and shown to be in general accord with the occlusion theory of heterogeneous polymerization. The effect of oxygen on the electron-resonance absorption is characterized by a rapid initial decrease followed by a slow decay. The results are tentatively interpreted in terms of the formation of peroxy and/or HO2 radicals. It is surprising that the absorption line obtained with polyacrylonitrile radicals does not show the fine structure which would be expected to arise from interaction of the unpaired electrons with hydrogen and nitrogen nuclei. A possible reason for this is discussed.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1959.1203412716
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