The first members of the series of poly‐m‐carboranylenesiloxanes were synthesized by the ferric chloride‐catalyzed condensation of methoxy‐ and chloro‐terminated monomers and generally obtained as insoluble crosslinked gums It has now been discovered that long‐chain, linear polymers can be prepared by simple hydrolytic condensation of m‐B10H10C2(SiMe2OSiMe2Cl)2 and m‐B10H10C2(SiMe2OSiMe2OSiMe2Cl)2 at ice bath temperature, as well as by acid‐catalyzed condensation of the corresponding silanols. In addition, phenyl‐substituted copolymers have been obtained which show outstanding thermo‐oxidative stability at elevated temperature. These linear polymers are soluble waxes and liquids with molecular weights between 16,000 and 30,000; they are potentially useful as high‐temperature liquids and coatings and can be cured at room temperature to form elastomers.

A series of linear trifluoropropyl‐substituted polycarboranylenesiloxanes with molecular weights between 3,500 and 13,000 has been prepared by the tetramethylguanidine–sulfuric acid‐catalyzed condensation of various silanol‐terminated monomers as well as by simple hydrolytic condensation of m‐B10H10C2(SiMePfOSiMePfCl)2 and B5H5C2‐(SiMePfCl)2 (where Pf = CH2CH2CF3). The polymers containing the C2B5H7 and C2B10H12 carboranes range from hard glasses to viscous gums and rubbers, are more thermally stable than fluorinated silicones with comparable resistance to solvents, and are potentially useful as high‐temperature fuel tank sealants.

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