Application of Radical Cage Reactions in Studies of Microstructures of Polymers and Composites -[103 refs.]. -(DAVYDOV, E. YA.; VOROTNIKOV, A. P.; PUSTOSHNYI, V. P.; PARIISKII, G. B.; Russ. Chem.
The character of nonexponential kinetics of the low-temperature decay of triplet carbenes in polymers has been given consideration. The temperature dependencies of the decay rate and the kinetic isotope effect were found at 77-180 K. The controlling factor in the kinetic nonequivalence of carbenes is the distribution of distances of the hydrogen atom tunneling from the matrix molecules. The effect of magnetic field on the rate of the carbene decay has been seen at 77 K. On the basis of the magnetic dependence view, the mechanism of the carbene decay involving spin and chemical dynamics of intermediate short-lived radical pairs has been advanced. The nature of magnetic effect in polymers shows the configuration inhomogeneity of radical pairs.
The mechanism of reactions of nitrogen dioxide with polyvinylpyrrolidone at 295-363 K has been considered. The nature of the molecular and free radical products of reactions has been studied by UV and ESR spectroscopy. The main molecular products are nitrites and nitrozoamides. The formation of stable acylalkylnitroxyl and iminoxyl radicals was registered. The influence of the structural-physical modification of the polymer at filling by aerosil has been established on kinetics of the formation of radicals.
Overlayers of a fatty acid (palmitic and lauric acid) formed at the interface between a solution of this molecule in phenyloctane and the basal plane of graphite are studied by in situ scanning tunnelling microscopy. The layers organize into lamellae, which are formed by a close packing arrangement of molecules parallel to the graphite surface. Chemical modification of the STM tips used allowed identification of the functional group. Indeed, the gold tips used are functionalized with 4-mercaptobenzoic acid (4-MBA) and 4-mercaptotoluene (4-MT). The same functional group on a sample is then 'seen' as a dark and a bright spot when imaged with 4-MBA and 4-MT modified tips, respectively. This contrast distinction is related to interactions (or a lack of them) between the carboxyl group on the sample and molecules on the tip, which can facilitate (or hinder) the electron tunnelling.
The comparison between traditional and grafted antioxidants shows that grafted antioxidants has qualitative advantages. DTBP produces the most promising results in the study. The results suggest that hindered phenols grafted by carbene synthesis on macromolecules will stabilise P.I. and other elastomers.
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