Carborane-siloxanes synthesis

The original FeCl3-catalyzed condensation reaction strategy has been exploited recently by Patel and co-workers for the synthesis of poly(m-carborane-siloxane) rubbers (103) (Fig. 63) in the reactions between dimethoxy-m-carborane terminated monomers and dichlorodimethylsilane.131 They have also synthesized similar polymers... 

One of the earliest and most popular systems investigated are the highly heat-resistant poly(w-carborane-siloxane)s. A review of the general literature on the methods used in the synthesis of these materials is reported in the following sections. 

After synthesis, the modified carborane-siloxane gums were fabricated into shaped components using standard siloxane vulcanization and fabrication technology. Di-chlorobenzyl peroxide (1% by wt) was used as the cross-linking agent and mixed into the polymer formed in scheme 7. Shaped rubber components were readily prepared by compression molding operations at 70°C. Postcure operations were typically at 120°C for 24 hours. 

At AWE, the Lewis acid-catalyzed bulk polymerization route has been the main synthesis route to poly(m-carborane-siloxane) elastomers. Our selection has been based on considerations of safety, availability of key reagents, and ease of scale-up operations. An understanding of the physical and chemical properties of these materials, and how these properties can be modified through the synthesis process, is essential in order to develop materials of controlled characteristics. 

The strong interest in poly(carborane-siloxanes) is primarily due to their thermal stabilityThe synthesis of elastomers with a 50°C gain in the use temperature over corresponding polysiloxanes has been a technical success, yet, owing to their high cost, industrial applicability is doubtful. They are synthesized by condensation of the carborane-siloxane halide with a diether ... 

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. 

The first class of polymers which will be discussed is not a true silarylene polymer, but is presented here because its synthesis has led to a number of the silarylenesiloxane polymers discussed previously. These polymers are known as poly(dodecacarborane-siloxanes), the study of which has been reviewed by Peters. The carborane molecule is very interesting and becomes an entire topic in and of itself. For the sake of completeness, the... 

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