The paper discusses the specific features of thermal behaviour of carborane-containing polymers and the stabilizing effect of the carborane groups as exemplified by arylene carboranes. The results obtained explain as a whole the stabilizing effect of aromatic polymers by carborane-containing additives.At the present time the requirements for a prolonged thermal stability of polymers, the working temperatures of the corresponding composites, considerably exceed those of the stability of chemical groups and chemical bonds which form even the most thermally stable polymers (cyclo-chain polyheteroarylenes, polyorganosiloxanes). The stabilizers of thermal and thermal-oxidative degradation acting by the known classical mechanisms cannot be effective at 350-40O0C, at least for a prolonged time. At the same time it has sufficiently long been established in practice that the polymers with carborane-12 groups in the macromolecule make it possible to achieve higher working temperatures of polymeric materials.'A sufficient number of papers dealing with investigations and explanations of the specific features of thermal behaviour of carborane-containing polymers and the stabilizing effect of the carborane groups was published. But most often the conceptions developed in them are either of purely phenomenological or of insufficiently well-founded, hypothetical character due to complex investigations of chemical transformations especially in three-dimensional polymeric matrix. The present lecture reports the results of investigations on the mechanisms of carborane-12 transformations by the action of high temperatures and oxygen that can explain this unusual thermal behaviour of carborane-containing polymers and formulate a general approach to stabilization of polymeric materials intended for operation at elevated temperatures.In the last two decades almost all known classes of polymers containing carborane-12 groups in the backbone or as side groups have been prepared. Investigations of their properties showed that the introduction of carborane groups into the polymer chain increases polymer thermal stability and their composites, this showing itself most effectively in case of aromatic polymers. A similar result can be achieved by introduction of carborane-containing additives into polymers primarily such as aromatic derivatives. Thus it can be said about the effect of carborane-12 groups stabilizing thermal and thermal-oxidative degradation of aromatic polymers.In the behaviour of carborane-containing polymers under the action of elevated temperatures and oxygen a number of specific features can be marked which differentiate them from that of their ordinary analogs. For instance, under conditions of thermal-oxidative degradation the chemical transformations in the matrix of carborane-containing polymers are observed in most cases at lower temperatures (200-350°C) that allows for classifying them as thermostable polymers in the adopted meaning of this word.' Unusual small weight losses at high temperatures is the second most e...

The diamagnetic shielding of nuclei by Bloch electrons in a metal is considered. The shielding may be divided into a Lorentz correction arising from a uniform magnetization and a part due to the induced volume currents. An exact expression in the Bloch model is derived for the volume current density induced in a metal by a uniform magnetic field. This permits in principle the calculation of the shielding. Certain special cases are discussed. §

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