[en] The formation of paramagnetic species in the radiolysis of styrene-butadiene block copolymers and inter polymers of polystyrene and polytrichlorobutadiene was studied at 77 K using ESR spectroscopy. The results obtained reveal substantial non-additive effects in the radical yields. In the case of inter polymers, the observed yields are higher than the expected additive values (sensitization), whereas in the case of block copolymers the effect has the opposite sign (protection). The analysis of paramagnetic species demonstrates that the observed peculiarities result from interphase migration of electrons followed by their reactions with chemical traps (chlorinated groups or neutral radicals). It was concluded that the long-range reactions of electrons were controlled by electronic characteristics of micro phases.

[en] Complete text of publication follows. The studies of radiation-chemical behaviour of isolated organic molecules in rigid inert media are of considerable interest for radiation chemistry and general structural chemistry. Previous efforts were limited to the ESR studies of radicals resulting from some small hydrocarbon molecules in frozen rare gas solutions. Recently, we developed an approach to the radiation chemistry of isolated organic molecules using classic matrix isolation procedure for sample preparation and a combination of ESR and IR spectroscopy for characterization of paramagnetic and diamagnetic species resulting form electron irradiation or organic molecules in solid rare gas matrices at 10-15 K. The results obtained reveal high efficiency of energy transfer from rare gas matrix to organic molecules. The total radiation-chemical yields of degradation of organic molecules in argon and xenon matrices were measured directly by IR spectroscopy. The studies of the effect of electron scavengers on the radiolysis of organic molecules in solid rare gases show that the main primary process is positive hole transfer from matrix to additive molecule. ESR spectra of a number of radical cations (alkanes, ethers, arenes) were first characterized in a low-disturbing environment. It was found that the electronic characteristics (IP, polarizability) of the matrix used had crucial effect on trapping and degradation of primary organic radical cations. Using matrices with various IP provides an unique possibility to examine the chemical meaning of excess energy resulting from exothermic positive hole transfer, that is, to follow the fate of excited cations in condensed phase

[en] The selectivity of formation of primary radicals in irradiated solid hydrocarbons and related polymers is analyzed on the basis of ESR studies at low and super-low temperatures. The first direct experimental evidence for selective localization of the primary alkyl radicals at conformational defects (gauche conformers) was obtained for high-density oriented polyethylene irradiated at 15K. This result implies highly selective primary C-H bond rupture, which correlates with the structure of the ionized molecules of linear alkanes. The correlation between the spin density distribution in the primary hydrocarbon radical cations and the initial mode of radical formation in the corresponding polymers is discussed. (author)

[en] Long-range electron effects are responsible for specific localization and selectivity of the radiation-induced chemical transformations occurring in molecular solids and polymers, when the classic diffusion mobility is essentially restricted. In particullar, understanding of the effects of this kind may be of key significance for establishing new ways to control the radiation sensitivity of macromolecules and organized polymeric systems, nanomaterials and biopolymers. This talk will present an overview of model studies of the long-range electron effects with the characteristic scale from several angstroms to ten nanometers. The following aspects of the problem will be analyzed: (1) Positive hole delocalization in ionized molecules. This phenomenon has been demonstrated experimentally and confirmed by quantum chemical calculations for a number of various-type molecules (alkanes, conjugated polyenes, bifunctional compounds). The effective delocalization length was found to be up to 2 nm (or even larger). The role of this effect in site-selective radiation chemistry will be discussed in the frame of concepts of distributed reactivity and 'switching' between delocalized and localized states. (2) Trap-to-trap positive hole and electron migration between isolated molecules or functional groups. The characteristic distance for this process was estimated to be 2 to 4 nm. Special impact will be made on the possible role of this process in selection of specific isomers or conformers upon irradiation of complex systems and macromolecules. (3) The effects of long-range scavenging of low-energy secondary electrons in polymers and organized polymeric systems. As revealed by model experiments, the radius of electron capture in solid polymers may be in the range of 1 to 10 nm. Possible implications of scavenging effects for controlling the radiation chemistry of polymers and organized polymeric systems will be considered

[en] Positive hole transfer between alkyl benzene molecules dispersed in frozen solutions in halocarbons (Freons) was studied by EPR. It was found that efficient trap-to-trap transfer occurred between various solute molecules, if the difference in ionisation potentials exceeded ca. 0.3 eV. In the case of small IP differences, the direction of positive hole transfer may depend on the molecule conformation and other 'subtle' effects

[en] ESR spectra of γ-irradiated solutions of acetic and propionic aldehydes in freon-11 and freon-113 affected by aldehyde concentration, temperature, and the action of light were studied. It is shown that the radical cations are converted into neutral radicals, and the cations CHsub(3)CHsub(2)CHOsup(+). are converted to RCO and CHsub(3)CHCHO due to ion-molecular reactions of proton transfer of hydrogen atom transfer. (author)

[en] ESR spectra of γ-irradiated acetone and CH₃COEt solutions (0.1-22%) in CFCl₃ were studied. The yields of monomer and dimer radical cations of ketones and RCHCOCH₃ radicals depend on ketone concentration in CFCl₃. When exposed to light the dimeric radical cations are transformed into RCHCOMe, while the monomeric radical cations disappear without further radical production. Different types of solid phase ion-molecular reactions for monomer and dimer radical cations are discussed. (author)

[en] The effect of 2-propanol on radical yields in γ-irradiated acetone has been studied by spin-trapping method. 2-propanol has proved to suppress the CH₂COCH₂ and CH₃ yields and to increase the (CH₃)₂COH yield. The results are explained by the ion-molecular reaction between acetone primary cation and 2-propanol. (author)

[en] Short communications

[en] The ESR spectra of γ-irradiated solutions of acetic acid and acetic anhydride were studied depending on their concentrations in CFClsub(3). The structure of thus produced radical cations is confirmed with the deuterium substituted analogues. It is shown that the ion-molecular reaction of the radical cation CHsub(3) COOHsup(+) in the isolated dimer takes place for the dilute solutions of acetic acid in CFClsub(3) resulting in the formation of CHsub(3)COO followed by its decomposition to CHsub(3) + COsub(2) while the radicals CHsub(2)COOH are formed via secondary processes. The reactions of radical cations of acetic oxide were also studied. (author)