G.B. Pariiskii

An electron paramagnetic study of the formation and photochemical reactions of macroradicals in polycaproamide under the influence of light

The effect of the spectral composition of the light on the nature of the macroradicals formed has been studied by the EPR method at low temperatures, with orientated films of polycaproamide (PA). It is shown that on irradiation of PA with ultraviolet light ∼(CH2)5—C=O radicals are formed and that these undergo photolysis in visible light with elimination of CO. The nature of the radicals formed and the laws of their formation and mutual reaction under the influence of light of different spectral composition, not absorbed by the polymer, has been studied in PA containing added FeCl3. It is shown that five types of macroradicals are formed and the structure of four of them has been established. It is concluded that degradation of the polymer molecules initiated by FeCl3 involves formation and photochemical conversion under the influence the influence of light of λ ∼ 370 nm of ∼ ∼ radicals. A scheme of the thermal and photochemical reactions of macroradicals in PA is proposed.

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.

Kinetic study of thermal decomposition of benzoyl peroxide in polyamide and degradation of polymer macromolecules

A kinetic analysis was made of the thermal decomposition of benzoyl peroxide in polyamide in inert atmosphere. It was established that the decomposition of peroxide takes place simultaneously by monomolecular and chain mechanisms. Chain decomposition of benzoyl peroxide is induced by polymer macromolecules and the order of the reaction is 12. Thermal decomposition of benzoyl peroxide in polyamide causes decomposition of polymer macromolecules. It was shown that macromolecular rupture does not involve the induced decomposition of peroxide.

Photo-conversions of free ester group radicals of polymethylmethacrylate☆

Abstract ESR is used to study the photoconversions of the free ester group radicals of polymethylmethacrylate (PMM) which form in the polymer during the photo-reduction of added ferric chloride at low temperatures. An effective photo-dissociation of the ∼CH 2 C(CH 3 ) (COOCH 2 )CH 2 ∼ radicals which takes place on exposure to light of γ 2 C(CH 3 )··(C = O)CH 2 ∼ radical to form. Light of 400 γ 2 C(CH 3 )CH 2 ∼ radical. The latter was recorded for the first time in PMM and its parameters in the ESR spectrum determined. The HCO radicals forming during the photolysis initiated with ferric chloride under UV light are the conversion product of the primary radicals, and their yields increase on reducing the wavelength of the light.

The effects of ionol and oxygen on the benzoyl peroxide initiated thermal degradation of polyamide

Abstract The effects of ionol and oxygen on the thermal decomposition of the benzoyl peroxide in polyamide and on the degradation of the polymer have been studied. The process is complex in an inert atmosphere and consists of primary decomposition of the initiator as well as of initiated decomposition reactions of first and half order with respect to the peroxide concentration. The degradation of the macromolecules was found to be highly efficient when free initiator radicals acted upon the polyamide. The Ionol reduces the rate of the benzoyl peroxide initiated thermal degradation of the polymer. The formal kinetics and the mechanism of reaction which explain the observed process kinetics are described.

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.

Kinetic features of the photoreduction of ferric chloride in solid polymethylmethacrylate

Abstract A kinetic study has been made of the photoreduction of ferric chloride additions in solid PMMA under the action of light with λ = 313, 365 and 405 nm at 77 and 293°K, and the kinetics of the accumulation of macroradicals at 77°K ( λ = 365 nm) have been investigated. The kinetics of the processes are determined by a certain distribution in the magnitude of the quantum yields of the consumption of initiator whereby it is possible to describe regularities of the reactions examined from a single viewpoint on a quantitative basis. The quantum yields of the photoreduction of initiator and the formation of radicals have been determined as well as the values of the parameters of distribution according to the magnitude of the quantum yields. It is concluded that the distribution stems from the occurrence of dark stages during photoreduction of the additive in the polymeric matrix that is non-uniform in respect to its properties.

Formation of nitroxyl radicals during polyamide transformations initiated by peroxides

Abstract The formation in polyamide of two types of stable nitroxyl radical in polyamide radical transformations initiated by peroxides was established by ESR in inert atmosphere and in oxygen. From kinetic regularities of transformations of nitroxyl radicals and initiators it was concluded that the distribution of peroxide in polyamide is microheterogeneous and that this microheterogeneity influences the processes observed.

ESR analysis of the thermal and thermooxidative degradation of polyamidoimide films

Abstract The emergence of free radicals of polyconjugated systems (PCS) in the thermal and thermooxidative degradation of polyamidoimide films was observed in the temperature range 553–673°K. According to the ESR spectra these radicals are practically identical in character. The rate of accumulation and the limit concentrations of these PCS radicals are significantly higher in the thermal oxidation as compared with thermal degradation processes. This is attributable to a difference in the rates of formation of isoimide rings and in their limit concentrations in these processes. In the case of thermal oxidation the kinetic curves of accumulation of PCS radicals are described by a model of kinetic nonequivalence of reactive centres in solidphase radical reactions. Effective rate constants and activation energies have been determined for the accumulation of PCS radicals during the thermal oxidation.

Mechanism of reactions initiated by thermal decomposition of benzoyl peroxide in polyamide

A study was made of the effect of 2,6-di-tert-butyl-4-methylphenol and 2,4,6-tritert-butylphenol on kinetic regularities of thermal decomposition of benzoyl peroxide in polyamide and macromolecular breakdown in oxygen. A formal kinetic description was proposed for transformations in the system for inert atmosphere and oxygen atmosphere.