Carboranylenesiloxane polymers

While the Olin efforts on the production of high-temperature polymers were centered mainly on FeCl3-catalyzed condensation reactions, subsequent efforts from Union Carbide, Inc. utilized an aminosilane route and a ureidosilane route (Fig. 3) to synthesize carboranylenesiloxane polymers of high molecular weights. Using the former route, the polymer was produced by a condensation reaction between a carborane-disilanol and bis(dimethylamino)dimethylsilane, during which an expulsion of a... 

Figure 3 Reaction schemes for the aminosilane (top) and the ureidosilane (bottom) routes for the synthesis of carboranylenesiloxane polymers. (Adapted from ref. 23.)...

The Union Carbide team also utilized the dilithiocarborane chemistry to produce carboranylenesiloxane polymers by the metal-halogen interchange reaction (Fig. 4) between dilithiocarboranes and dichlorosiloxanes.21 Polymers with molecular weights up to 52,000 were synthesized by this procedure. 

The most studied class of boron polymers containing boron-silicon bonds are the carboranylenesiloxane polymers. The history of these polymers was discussed at the beginning of this chapter. The more recent advances in this group of polymers and in silicon-containing borazine and boroxine polymers are discussed in later sections of this chapter. In this section, some remaining groups of silicon-containing boron polymers are discussed. 

The synthesis of block polymers of diacetylene-silarylene and diacetylene-carboranylenesiloxane polymers (99a-e) (Fig. 61) by the polycondensation reaction of 1,4-dilithiobutadiyne with l,4-bis(dimethylchlorosilyl) benzene and/or l,7-bis(tetramethylchlorodisiloxane)-m-carborane have been reported by Sundar and Keller.129 These polymers are a hybrid between the carboranylenesiloxane and silarylene-siloxane polymers and have high char yields (up to 85%) at 1000°C in N2 and in air, reflecting the thermal stabilizing effects of the carborane and aromatic units in the polymeric backbone. 

Figure 61 The hybrid silarylene-siloxane/carboranylenesiloxane polymers, 99a-e.

Carboranylenesiloxane Polymers Containing Thermally Crosslinkable or Vulcanizable Diacetylene Groups... 

The linear polymers were readily formed by both methods. A salient feature in both of the syntheses was the in situ production of a desired carboranylenesiloxane oligomer by the reaction of a lithiated carborane and a chlorinated siloxane species rather than the use of the commercial Dexsil monomer as in the case of Henderson et al. [25] and Houser et al. [29], This has afforded an enormous degree of variation in the compositions of diacetylene-containing carboranylenesiloxane polymers that is not available by the conventional route of Henderson et al. [25]. The effect of the reduction in the diacetylene concentration was apparent in the positions and the intensities of the DSC peak maxima of the crossUnking endotherms of 5a-c. Thus, it was observed that as the concentration of the diacetylene units in the polymer... 

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. 

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