G.Ye. Zaikov

The mechanism of formation and decomposition of polyimides

Abstract The mechanism of formation of polyimides by two stage polycondensation of dianhydrides of tetracarboxylic acids with diamines in examined. It is shown that the characteristic features of this complex process, which is a combination of successive and parallel reactions, are mainly caused by the instability of the polyamido-acids formed in the first stage.

Sorption of water by aliphatic polyamides. Review

The published findings on the diffusion and solubility of water in aliphatic polyamides are systematized. Attention is focused on the influence of the chemical nature of the polyamide and its supramolecular structure on the sorption capacity and the diffusion and swelling coefficients. From perusal of the existing ways of predicting the values of solubility S and diffusion D coefficients in polyamides the authors propose a scheme for calculating S and D on the basis of only the structural formula of the polymer chain. The results may be used in study of the hydrolytic stability of the polyamides and prediction of their physiochemical properties on sorption of water.

The effect of mechanical loads on the low temperature oxidation of polymers and the effect of ozone-oxygenous action on isotactic polypropylene☆

A study has been made of the effect of mechanical loads on the rate of low-temperature oxidation of isotactic polypropylene by an ozone-oxygen mixture. It is shown that loading increases the rate of chemical degradation of PP. An essential difference has been detected in the character of dependences of the rate of accumulation of carbonyl groups on stress and strain. Under a regime with σ=const the main factor is the presence of overstrained bonds whose reactivity is higher. A superposition of three factors takes place with e=const: the presence of residual stress, increase in the kinetic flexibility of macrochains and an alteration in the orientation of chain segments.

Interaction of polyethylene with ozone

The presence of ozone in air, even in very small concentrations, markedly accelerates the ageing of polymeric materials [1]. It has been shown that the processes by which ozone acts on saturated polymers are accompanied by the intensive formation of oxygen-containing compounds, by a change in the molecular weight and by impairment of the mechanical and electrical properties of the specimens [2, 3]. The present work is devoted to the study of the kinetic laws and the mechanism of oxidative degradation of polyolefins in the solid phase under the action of ozone at temperatures below 100°C. Polyethylene (PE), which is made up of regularly alternating CH2 groups all of one type, and which does not contain side substituents, was used as the model compound: this made it possible to assess more unambiguously the characteristics of the reactions occurring during oxidation from the experimental data.

On the molecular mobility of polypropylene chains in amorphous regions of the stressed polymer

Abstract The segmental mobility in amorphous regions of isotactic PP subjected to mechanical loading has been investigated by ESR, using the stable nitroxyl radical (probe) 2,2,6,6-tetramethylpiperidine-1-oxyl. A complex relation between the correlation time τ for the probe and the degree of stress has been found. The value of τ decreases during the initial stage of loading and thereafter increases gradually, reaching a maximum under strains of ∼11%. It is surmised that the experimentally observed dependence is determined by an additional orientation of the specimen and by increasing segmental mobility of PP macromolecules accompanying increased stress.

Oxidative degradation of polymers under load. Ozone-oxygen action on oriented polyethylene

Abstract A study has been made of the influence of external loads on the rate of ozone oxidation of oriented high- and low-density polyethylene specimens, under regimes of constant stress and strain. It is shown that tensile stress has an accelerating effect on the kinetics of H atom abstraction. The higher sensitivity to loading of low density PE specimens compared with high density specimens is noted, and a relationship between loading sensitivity and MWD is observed for PE.

The study of the kinetics of formation of poly(amido) acids for carding

The kinetics of formation of poly (amino)acids based on carding diamine-9,9-bis-4′-aminophenylfluorene and 3,3′,4,4′-tetracarboxydiphenylsulphonic acid dianhydride (I), the dianhydrides of 3,3′,4,4′-tetracarboxybenzophenone (II), pyromellitic acid (III), 2,3,7,8-tetracarboxy-10,10-dimethylphenoxasilene, 3′,3″,4′,4″-tetracarboxydiphenyloxide, 3,3′,4,4′-tetracarboxydiphenyldimethylsilane, or 1,4-bis-(3,4-dicarboxy-α-cumyl)benzene, in N-methyl pyrollidone (MP) were studied by UV spectroscopy as changes of the amino group concentrations. The reaction rate has been found to increase on changing from the less polar solvent (dioxane) to the more polar MP, and also when water and carboxylic acids were added. The use of the more reactive anhydrides I, II or III was found to increase the rate of the main as well as of the secondary reactions, for example those with MP.

Changes in the melting temperature, polydispersity and crystallinity of the components in a blend of high density polyethylene with polypropylene at deep ozone oxidation☆

Abstract The melting of oriented samples of a HDPE-PP blend oxidized with ozone was investigated by the DSC method. The obtained values of the melting temperatures of HDPE and PP crystallites, the degrees of crystallinity of the components and the half-widths of the melting peaks of a HDPE-PP blend are compared with the corresponding values of these parameters in unoxidized blends. Ozone practically does not penetrate the PE crystallites in the blend, but it destroys the crystalline structure of PP in the blend up to its complete disappearance in composites with a low PP content.

Effect of ozone on saturated polymers. Review

Abstract The main processes occurring on exposure of saturated polymers to ozone and their possible applications in scientific research and technology are considered. It is shown that the reaction of ozone with the CH bonds of the macromolecules is accompanied by the formation of carbonyl and peroxide functional groups which accumulate parallel and independently of one another. As intermediate products, peroxide radicals are present in the system. The kinetics and mechanism of the processes of interaction of ozone with the macromolecules in solution and in the solid phase are discussed.

Some kinetic features of radical and ionic reactions in solid polymers

Abstract In this report concerning the effect of the rate of structural transition and intensity of molecular motion in a polymer matrix on the rate of radical reactions the causes of high activation energies and pre-exponential factors in experimental constants of bimolecular reaction rates were examined and the types of “gradual” reactions in solid phase were investigated. A study was made of the effect of plasticizing additives on relations of radical reactions, the anti-radical activity of antioxidants in a solid polymer, features of the mechanism of chain extension and breakage, the role of surface effects in breakdown and critical effects in decomposition of solid polymers. Features of the diffusion of electrolytes in a polymer matrix were described.