Mechanism of free-radical degradation of poly(amidoimide) in the presence of nitrogen dioxide

The mechanism of free-radical transformations initiated in poly(amidoimide) by nitrogen dioxide was considered. As was shown by EPR spectroscopy, interaction of nitrogen dioxide with amide groups of macromolecules results in the formation of iminoxyl and acylarylnitroxyl radicals. The iminoxyl radicals are the products of the reaction between nitrogen dioxide and the end groups formed in the course of degradation of macrochains. The formation mechanism of iminoxyl radicals was confirmed by the results of the study of the reaction between nitrogen dioxide and n-quinone, which models the structure of the end groups of poly(amidoimide) molecules, The degradation rate of the polymer was evaluated from the formation kinetics of iminoxyl radicals.