I. S. Gaponova

Ion-radical mechanism of polymer-nitrogen dioxide interaction

By the example of poly(2-vinylpyridine), the ion-radical mechanism is established for the generation of stable nitrogen-containing radicals in polymers under the effect of nitrogen dioxide. The mechanism includes the reactions of nitrogen dioxide dimers occurring in the form of nitrosonium-nitrate ion pairs. The ion-radical process is induced by electron transfer from donor groups of macromolecules to nitrosonium cations that results in the formation of cation-macroradicals and nitrogen oxide. Stable radicals are generated in the course of subsequent reactions of these particles and lead to the formation of macromolecular nitroso compounds, which are efficient spin traps.

Generation of nitroxyl radicals in reactions of nitrogen dioxide with p-benzoquinones

The formation of oxynitroxyl radicals has been observed by EPR in the course of exposure of p-benzoquinones to nitrogen dioxide. This process involves addition of nitrogen dioxide to the double bond system of quinones. Thermal conversion of oxynitroxyl radicals lead to the formation of acyl(alkyl)nitroxyl and iminoxyl radicals along with molecular nitration products. Kinetics of the oxynitroxyl radical formation depending on the nitrogen dioxide pressure has been defined. The temperature dependence of stationary concentrations of oxynitroxyl radicals at 230–310 K is determined by the equilibrium between the monomer and dimer forms of nitrogen dioxide. Nitrogen tetraoxide was found to initiate radical formation in p-benzoquinones.

Kinetics of formation of peroxide radicals in the ozonolysis of solid polystyrene and polyvinylcyclohexane

Abstract The EPR methods has been used to investigate kinetic regularities of the formation and decay of peroxide radicals in the ozonolysis of solid polystyrene and polyvinylcyclohexane. It is shown that peroxide radicals are formed mainly through interaction of ozone with an intermediate product, and not with CH bonds in polymer. A kinetic scheme is suggested for the process and the macroscopic reaction rate constants have been determined.

Aminoxyl radicals as crosslinks for macromolecules of polyvinylpyrrolidone.

Using polyvinylpyrrolidone as an example, it has been shown that photolysis of ceric ammonium nitrate at room temperature can result in crosslinking of macromolecules. This process correlates with the formation of stable aminoxyl radicals, which are registered by EPR. The mechanism involves photodissociation of nitrate radicals produced in the primary reaction into nitric oxide or nitrogen dioxide depending on the wavelength of the light, and simultaneous formation of macroradicals. The accumulation of aminoxyl radicals occurs owing to the acceptance of macroradicals by nitroso or nitro groups according to which mechanism of the nitrate radical photodissociation prevails. Similar radical reactions are observed in N-methyl-2-pyrrolidone.

POLYMERS IN POLLUTED ATMOSPHERE. MECHANISM OF RADICAL CONVERSIONS ON EXPOSURE TO NITROGEN OXIDES

Nitrogen oxides play a significant role in chemical processes taking place in an atmosphere and affect on an environment. The researches of the mechanism of nitrogen oxide reactions with polymers are important for evaluation of stability of these materials in polluted atmosphere. These researches can be also used for development of methods of the polymer modification, for example, for preparation of spin—labelled macromolecules. Most important for reactions with polymers are NO, NO2, NO3 as well as NO2 dimers. The features of the mechanism of reactions of these oxides with a number of polymers are considered. The especial attention is given to the mechanism of primary reactions of initiation and intermediate stages of complex radical processes under the action of nitrogen oxides. Nitric oxide does not react directly, but it recombines with free macroradicals formed in polymers by UV photolysis or γ—radiolysis. The nitro compounds formed in the subsequent reactions are converted into stable nitrogen—contai...

Decomposition of polypropylene hydroperoxides induced by nitric oxide: New concept of reaction mechanism

NO-induced decomposition of hydroperoxides in solid polypropylene and cumyl hydroperoxide, dissolved in n-decane, at 25°C was studied. Analysis of kinetic regularities of hydroperoxide decomposition and nitroxide radical accumulation leads to the conclusion that both in solids and in solutions these reactions have the autoaccelerated character. The induction periods are determined by trace amounts of impurities (probably of higher nitrogen oxides).The maximum rate of the process depends on the NO pressure. The possible reaction mechanisms are supposed, and the key role is assigned to the formed nitrosocompounds.

Interaction between polymers and polluted atmosphere (nitrogen oxides)

Abstract The mechanism of reactions of nitrogen oxides with various solid polymers has been considered. The active participants of the reactions with nitrogen oxides are double bonds, amide groups of macromolecules and peroxy macroradicals. The reactions of nitrogen oxides provide a simple way for the preparation of spin labeled polymers. The structure of the reaction front during nitration of polyisoprene has been studied using the ESR tomography technique. The structural-physical effect on kinetics and mechanism of reactions of nitrogen oxides has been demonstrated by the example of filled polyvinylpyrrolidone.

ESR study of nitrogen-containing radicals formed on photolysis and radiolysis of solid polymethylmethacrylate and cellulose triacetate in a nitrogen oxide atmosphere☆

Abstract It has been established that on photolysis and radiolysis of solid PMMA and CTA in an atmosphere of nitrogen oxide at room temperature stable macromolecular nitrogen-containing radicals of three types form: acylalkylnitroxyl, dialkylnitroxyl and iminoxyl. An analysis of their ESR spectra is presented and the possible paths of their formation discussed. A link between the nature of the radicals formed and the molecular dynamics of the polymers is noted.

Formation of macromolecular iminoxyl radicals during radiolysis of fluorinated polymers in nitrogen dioxide as medium

Nitrogen-containing radicals formed in solid PTFE and in a copolymer of tetrafluoroethylene with hexafluoropropylene under the action of γ-irradiation in the presence of NO are studied by an ESR method. It is concluded from the results of analyzing the ESR spectra of polymer powders and oriented films that iminoxyl radicals are formed under these conditions. In the case of PTFE the superfine interaction constants are determined together with the nitrogen nucleus and g-tensor components. The isotropic parameters are found for the copolymer of tetrafluoroethylene with hexafluoropropylene. A mechanism is proposed for the production of iminoxyl radicals, and the effect of molecular dynamics on the method of formation of nitrogen-containing macroradicals is discussed.

Thermal stability of tertiary peroxide radicals in the copolymer of tetrafluoroethylene with hexafluoropropylene

The ESR method was used to investigate the thermal stability of tertiary peroxide radicals in the copolymer of tetrafluoroethylene with hexafluoropropylene at 25–55°. Decay of these radicals accompanied by CO bond scission was observed. The effective equilibrium constant if the reaction O.2⇄kgk1R.tert+O2 was measured and found to be Keff = k1k2ks = 2·4 × 1013exp−)74500/RT mm Hg O2 where ks is the solubility constant for O2 in polymer. Rate constants were evaluated at room temperature for the direct and the reverse reactions.