Macroradicals, nitrogen-containing

Because of the low reactivity of pure NO in reactions of atom abstraction as well as addition to double bonds, direct interaction of this reactant with most synthetic polymers does not occur. However, the chemical modification of macromolecules in an atmosphere of NO in conditions of the simnltaneous generation of macroradicals takes place due to spin trapping via the formation of nitroso compounds. The structure of stable nitrogen-containing radicals formed from nitroso compounds in the subsequent reactions gives information on the mechanism of proceeding processes in polymers under the action of various radical-initiating factors. 

Exposure of fluoroalkyl macroradicals at 25-250 °C to NO does not produce nitrogen-containing radicals,... 

As has been established [45], one or both of the nitrogen-containing products and alkoxy radicals decompose at 90 °C at a significant rate to produce terminal alkyl macroradicals ... 

As discussed in Chapters 1 and 5, nitrogen dioxide (NO ) is a relatively low-active free radical. Therefore, it virtnally does not react at ambient temperatures with polymers that do not contain specific fnnctional groups. However, NO interacts very actively with the double C-C bonds of macromolecules as well as with macroradicals. These reactions result in the formation of various products of nitration and nitrosation. Subsequent processes can involve the degradation of macromolecules, and the formation of stable nitrogen-containing radicals. 

Our investigations suggest that grafted copolymers are obtained probably by the recombination reactions of the macroradicals generated both on the cellulosic support and on the nitrogen and phosphorus containing polymers. 

It can be presumed that under cold plasma conditions, the nitrogen and phosphorus containing polymers can lead also to the macroradicals through dehydrogenation of CH aromatic and aliphatic or NH groups. 

To predict the stability of fluorinated polymers in the atmosphere polluted with nitrogen oxides, the ratio of rates of peroxynitrates in polytetrafluoroethylene (PTFE) by two mechanisms has been determined [19]. Chain peroxide radicals R 02 were obtained by photolysis of PTFE powder in a vacuum with the subsequent oxidation of fluoroalkyl macroradicals. The end peroxide radicals R 02 were generated by photolysis of the R 02 containing PTFE in the air. The exposure of PTFE samples containing chain or end peroxide macroradicals to NO2 results in decay of these radicals. The kinetics of the decay of peroxide radicals of both types is practically identical, and is likely to be determined by the rate of diffusion of NO into the... 

A similar effect is observed for polymeric initiators containing nitroso groups in their main chain [233]. Upon absorption of two photons, nitrogen is released and initiating macroradicals are formed, as depicted in reaction (51). Care must be taken while working with nitroso-containing macroini-... 

---