Interaction of polypyromellitimide with nitrogen dioxide

The mechanism of interaction of nitrogen dioxide with aromatic polyimides is considered by the example of polypyromellitimide. The formation of stable radicals of acylarylaminoxyl, iminoxyl and phenoxyl types has been detected by electron paramagnetic resonance spectroscopy. Acylarylaminoxyl radicals were detected in polypyromellitimide after its exposure to nitrogen dioxide at room temperature followed by pumping nitrogen dioxide from the samples. Iminoxyl and phenoxyl radicals were formed during thermolysis of the nitration products of the polymer at 373 K. The proposed mechanism is based on the reaction of dimers of nitrogen dioxide in the form of nitrosyl nitrate. It was observed that intermediate radical cations and nitric oxide were formed in the primary reaction of electron transfer from the polyimide to nitrosyl nitrate. The subsequent cage reactions with participation of radical cations and nitric oxide give nitroso compounds and nitrates which are precursors of stable nitrogen-containing and phenoxyl radicals.