Abstract
During high-temperature (623–673 K) oxidation of polyarylenes (polypyromellitimide and polyphenylquinoxaline), the molecular oxygen is enriched in the18O nonmagnetic isotope and impoverished in the17O magnetic isotope. The isotope selection increases with the increase in the degree of conversion of oxygen. The spin-selective reaction responsible for the selection of the17O isotope is the addition of molecular oxygen to triplet exited aromatic fragments of macromolecules to give endoperoxides. This reaction, which is selective in terms of the electron spin, is also nuclear-spin selective resulting in a magnetic isotope effect. The selection of nonmagnetic isotopes,16O and18O, is caused by competition between the reversible and irreversible decomposition of endoperoxide and by the classical isotope effect in these reactions.
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