Polymer carborane, properties

The preparation of poly(m-carborane-siloxane) polymers has also been successfully achieved directly from the carborane monomer.22 The reaction used is shown in scheme 9. Here, the direct salt elimination reaction between dilithiocarborane and a dichlorosiloxane (e.g., 1,5-dichlorohexamethyltrisiloxane) results in the formation of linear polymers with a molecular-weight (M ) typically of 6800 dalton. However, the reported literature detailing this approach is very limited indeed, and the reaction has not found significant use. This is most probably because only relatively low molecular-weight polymers can be produced, ultimately restricting the flexibility to produce materials of controlled mechanical properties. 

Properties of carborane-siloxanes can be readily modified through changes in the polymer backbone and by the use of supplementary agents in order to optimize the property-performance profile for different use situations. 

Covering many areas of chemistry with boron at its centre, topics include applications to polyolefin catalysis, medicine, materials and polymers boron cluster chemistry, including carboranes and metal-containing clusters organic and inorganic chemistry of species containing only 1 or 2 boron atoms and theoretical studies of boron-containing compounds. New materials with novel optical and electronic properties are also discussed. 

Incorporation of carborane moieties into silicone chains also leads to improved thermal properties of such semiorganic polymers. The stationary phases based on carborane polymers have been available commercially since the early 1970 s, when the first analytical results were also reported [86] for some biological compounds. Although such phases were believed to be stable up to about 400°C, only moderately successful separations have been reported. While the carborane cages can be differently incorporated into siloxane polymers to influence their consistency, functional groups (phenyl, cyanoethyl, etc.) may also be varied to influence selectivity. 

Carboranes - polyhedral boranes containing carbon in the framework - have been known for over 35 years, and their intrinsic stability, versatility, structural variety, and electronic properties have been put to use in a number of diverse areas, [1] for example in the synthesis of extraordinarily heat-stable polymers, in BNCT (boron neutron capture therapy), as ligands in metallacarborane catalysts, as com-plexing agents for extraction of metal ions, as precursors to ceramics, conducting polymers, and nonlinear optical materials, as anticancer... 

Summary Carborane-hybridized silicon polymers were synthesized from the hydro-silylation reaction between diethynylbenzene-silylene polymers with reactive vinyl side groups and 1,7-bis(dimethylsilyl)carborane and l,7-bis(diphenylsilyl)carborane. Precise NMR spectroscopic studies show that the structures of these polymeres were quite complicated unreacted vinyl groups and pendant carborane substitution exist along with crosslinked carborane. These polymers show plastic moldability. Thermal treatment of the hybrid polymers gives excellent stability in both thermal and mechanical properties of the polymers. Their unreacted moieties seem to act as crosslinkable thermosetting features to make these polymers more stable. 

In the US and the Russian munitions field, carborane dicarba-c/oso-dodecaborane(12) [5] has been used to improve the properties of silicones. Some American companies have synthesized carborane-siloxane polymers as high temperature elastomers [6]. Lately, Keller s group has reported a diacetylene-carborane-siloxane system showing one of the highest stabilities in silicon polymers [7]. 

In the case of aU of the developed hybrid silarylene-siloxane and carboranylenesiloxane polymers, an evaluation of the nature of different phases containing aromatic or carborane groups will be illuminating to understand what contribution does each distinct phase has on the elasticity and other material properties of the generated networks. Other in-depth mechanical studies are also in order to better evaluate the high temperature elasticity of the materials. 

The interest in high-temperature elastomeric materials stems from the high demand for such materials for application in advanced technologies, particularly the aerospace, defense, and computer industries. Such materials are expected to have long-term thermal, thermo-oxidative and hydrolytic stability at and above 300 to 350 °C and to also have the ability to maintain pronounced flexibility to well below ambient temperature. The elastomeric crossUnked network polymers of carboran-ylenesiloxanes and silarylene-siloxanes described in this chapter possess similar properties and are therefore ideal candidates for a wide variety of engineering applications under unusual service conditions. In addition, these network polymers also have the utility in other applications that may or may not directly relate to their... 

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