A. P. Vorotnikov

Influence of Filler on Kinetics at Low-Temperature Conversion of Macroradicals

Abstract In poly(methyl methacrylate) and polyvinylpirrolydone the influence of aerosil on the kinetics of macroradical transformation at 120–220 K is established. The effect of filler is explained by the changes of the structural–physical properties of the polymer binder transformed into the interface state. From the kinetic data the effective thickness of interfaces is estimated.

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...

Effect of Polymer Matrix on Kinetics and Mechanism of Carbene Reactions

The features of kinetics and mechanism of the cage radical reactions initiated by carbenes in solid polymers has been considered. The peculiar low temperature reaction of arylcarbenes is their interaction in clusters with formation of biradicals (BR). The yield of BR is a measure of the distribution non-homogeneity of the carbene precursors in polymers. The reaction of BR formation allows us to study the molecular dynamics at cryogenic temperatures. The main factor determining the kinetic non-equivalence of triplet carbenes in low temperature reaction of the hydrogen atom abstraction is the dispersion of the cage distances between carbenes and C-H bonds of macromolecules. The strong effect of structural modifications in filled polymers on the thermal decay of carbenes has been established. The matrix effect on the mechanism of the product formation in the carbene reactions, associated with the relaxation processes, has been recognized by the example of the polyvinylalcohol cross-linkage. The advantage of polyisoprene stabilization against thermoxidation by the phenol grafting in carbene synthesis has been shown.

The Influence of Liquid Crystal Ordering on Reversible Radical Dissociation

Abstract The influence of liquid crystal ordering in nematic, smectic and isotropic phases on thermodynamic parameters of a reversible thermal dissociation of dimeric 2,2-bis[2-(p-dimethylaminophenyl)indan-1,3-dione] into two stables 2-(p-dimethylaminophenyl)indan-1,3-dione-2-yl radicals was investigated.

Kinetic features of radical dissociation in filled acetyl cellulose

Abstract The kinetic patterns of the diphthaloyl ethane dissociation in acetyl cellulose at 320–370 K with the formation of stable radicals have been considered as a function of the aerosil content. The profound filler effect was found to be upon the temperature dependence of the radical yield. Kinetic parameters of the radical dissociation are determined by the structural modifications of the polymer under shaping of interfaces.

Dynamics of Biradicals Formation by Low Temperature Conversions of Carbenes in Polymers

Abstract The kinetics of diphenylcarbene (DPC) conversions in clusters with biradicals (BR) formation has been studied in polycarbonate (PC) and polymethylmethacrylate (PMMA) at 77–125 K. The portion of carbene precursor-diphenyldiazomethane (DDM) iocalized in micropores has been evaluated from concentration dependences of BR yield. The correlation of kinetic parameters of BR low temperature formation with molecular dynamic properties of spin probe has been observed in studied polymers. The structural modification of PC by aerosil filling effects on conversion kinetics of BR.

Interaction of cyclohexadienone carbene with piperylene oligomer

Conclusions1.In the photodecomposition of p-benzoquinonediazide in a frozen matrix of piperylene oligomer, the formation of triplet cyclohexadienone carbene has been registered by means of ESR, along with allyl radicals of the matrix and phenoxyl radicals in the isolated state and in the form of radical pairs.2.When the carbene interacts with the matrix, it is inserted at C-H bonds of the macromolecules.3.A tunneling mechanism of H atom transfer has been proposed in the reaction of the carbene with the matrix. Estimates of the height and width of the potential barrier of the reaction are given.

Mechanism of transformation of diphenylcarbene into an oligomer of piperylene

Conclusions1.Formation of diphenylcarbene (DPC) and the radical pairs which arise as a result of migration of an H atom from the tertiary C-H bonds of the macromolecules into the DPC was recorded during photodecomposition of diphenyldiazomethane into an oligomer of piperylene by EPR at 77‡K.2.The process of thermal quenching of DPC passes through a stage of formation of radical pairs and is caused by migration of an H atom from the macromolecules of the matrix to the DPC by a tunnel mechanism.3.The kinetic principles of thermal quenching of DPC were explained by the distribution of the distances between the carbenes and C-H bonds in the macromolecules. The characteristics of this distribution of distances were estimated.