N. M. Livanova

Microstructures and supramolecular structures of butadiene-nitrile rubbers: Paramagnetic-probe study

The chain microstructures and supramolecular structures of butadiene-nitrile rubbers are studied by ESR spectroscopy. On the temperature dependences of the rotational mobility (correlation time τc) of paramagnetic probes differing in size (2,2,6,6-tetramethylpiperidine-1-oxyl and 4-benzoate-2,2,6,6-tetramethylpiperidine-1-oxyl), relaxation transitions are observed. It is shown that there is a correlation between the Arrhenius parameters of rotational mobility of radicals and the copolymer composition and that different brands of rubbers differ in microstructure and supramolecular structure.

The Structure of Polybutadienes and Butadiene-Acrylonitrile Copolymers

The paramagnetic probe method with the use of free radicals of different dimensions (2,2,6,6-tet-ramethyl-1-piperidinyloxy and 4-benzoate-2,2,6,6-tetramethyl-1-piperidinyloxy) has been employed to study the effect of the isomeric composition of butadiene units in polybutadienes and butadiene-acrylonitrile copolymers on the number and dimensions of ordered structures. The nature of density fluctuations and defective regions, that is, the regions in which the radicals are sorbed, has been ascertained. It has been shown that the ordered regions are composed of stereoregular chain fragments, while defective regions are enriched with butadiene isomers different from those present in prevailing amounts.

Ozone resistance of crosslinked blends of butadiene-acrylonitrile and ethylene-propylene-diene elastomers and interphase interaction in these blends

The relation of ozone resistance to the volume and structure of the interphase layer and the amounts of crosslinks in the interlayer was studied for covulcanizates of butadiene-acrylonitrile rubbers of various polarities with ethylene-propylene-diene (EPDM) elastomers that differed in the comonomer composition and stereoregularity of propylene units. It was shown that the ozone resistance is determined by the compatibility of the components, the interlayer volume and density, the amount of crosslinks in the interlayer, and the strength of the EPDM network.

The nature of sites of absorption of low-molecular-mass compounds by butadiene–acrylonitrile copolymers

The rotational mobilities of the paramagnetic probes TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and BZONO (4-benzoate-2,2,6,6-tetramethylpiperidine-1-oxyl) are studied via EPR spectroscopy and the equilibrium swelling of random and multiblock butadiene–acrylonitrile copolymers of various compositions and stereostructures of butadiene units in n-heptane, methyl acetate, and toluene are studied. The nature of defective regions sorbing low-molecular-mass compounds is ascertained. The rotational mobilities of the probes in defects of various structures are estimated. The sites of sorption are found to be identical in crosslinked and noncrosslinked elastomers. It is shown that the sorption of n-heptane and methyl acetate appears in the same defective regions as those of the TEMPO radical, while the sorption of toluene emerges in sorption sites where the value of free volume is sufficient for the sorption of the bulky radical BZONO. A decay in local molecular mobility in structural defects (“holes”) does not hinder the absorption of lowmolecular- mass compounds if the free volume is sufficient.

Effect of the structure of butadiene-nitrile elastomers on the ozone resistance of their vulcanizates

A comparative analysis of the ozone resistance of vulcanizates based on butadiene-nitrile elastomers with the same network density but different contents of acrylonitrile units is performed. The role of the orientation of chain fragments of vulcanizate chains during the reaction of double bonds with ozone is demonstrated.

Principal possibility of strength reinforcement of polypropylene during uniaxial elongation in an oxidizing medium

It was shown that isothermal curves of the durability of oriented films of isotactic PP at 120° and with PO2=600 torr are extremal in nature. Comparison of the concentration of carbonyl groups in the termination zone of samples with properties of the polymer under stress showed the role of variation of kinetics of oxidizing processes in the existence of non-monotonous dependence of durability on stress. PP is oxidized in the free and stressed state by a heterogeneous mechanism. The local nature of failure under conditions of thermal-oxidative breakdown was established. It was shown that the strength stabilization and strength reinforcement of the polymer are possible, in principle, in the oxidizing medium. A scheme was proposed for the fracture of the polymer under stress under conditions of thermal-oxidative breakdown.

Breakdown mechanism of stressed polypropylene in oxidizing medium. Structural effects

Abstract It was shown that thermal oxidation of mechanically stressed PP at 120–130° is of local nature. In the zone of future macroscopic breakdown a centre of oxidation is formed, which spreads in the film to a distance depending on external stress and the structure of the sample: the greater the stress, the more local is oxidation in the centre of breakdown. With fixed stress the concentration gradient of carbonyl groups in non-annealed samples is always higher than in annealed ones. It was shown that not only concentration but also the composition of carbonyl-containing groups in PP oxidized depends on stress, which enables the method to be recommended for detecting defects.

Fractional free volumes in structural defects of butadiene–nitrile elastomers of various polarities and rotational mobilities of nitroxyl radicals

The correlation between the magnitudes of the fast components of rotational mobility of the nitroxyl radicals (2,2,6,6-tetramethylpiperidine-1-yl)oxyl and (4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-yl)oxyl measured via EPR spectroscopy, the fractional free volumes in the structural defects of butadiene–nitrile rubbers and the related vulcanized rubbers, in which the nitroxyl radicals are sorbed, and a variation in this correlation with an increase in temperature are established.

Structure of the interfacial layer and properties of crosslinked heterophase blends based on butadiene-nitrile and ethylene-propylene-diene elastomers

The density of the interfacial layer and the number of formed crosslinks have been estimated by means of swelling in selective solvents for heterophase blends of butadiene and ethylene-propylene elastomers. Ethylene-propylene-diene elastomers are characterized by an increased content of ethylene units and diene groups, a higher degree of isotacticity of propylene chain fragments, and a higher Mooney viscosity at low stereoregularity of the propylene units. The effects of the above parameters on the interfacial interaction and the kinetics of ozone degradation of the diene matrix have been studied.

Focal character of oxidation and the scale effect in the longevity of oriented polypropylene

Abstract The role of mechanical stresses in the advent and development of foci of oxidation in stressed oriented samples of isotactic PP in conditions of intense oxidation has been investigated. It has been established that the foci of the highest speed of initiation of radicals pre-exist in the starting samples and are not produced by mechanical stress although the stresses influence the speed of spread of the reaction of oxidation from the primary focus of intense initiation over the polymeric matrix. The probability of the initiation foci entering the sample is determined by statistics as a result of which a marked scale effect is manifest in the longevity of the oxidized stressed PP films. For a low probability of entry into the sample of initiation foci longevity is increased several times without the introduction of inhibitors of chain oxidation.