Carborane modified materials

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. 

Carboranes, These are used in neutron capture therapy (254), and as bum rate modifiers in gun and rocket propellants. They are used as high temperature elastomers and other unique materials, high temperature gas—liquid chromatography stationary phases, optical switching devises (256), and gasoline additives (257). 

The data for the plot in Figure 2 was obtained using a PDMS polymer modified with a carborane unit. A schematic of the system is given in Figure 3. For this material there is no radiation effect on an interface and the plot is linear over the entire dose range. The development of an ageing model that provided a predictive capability and high confidence is far easier in a system that displays a linear trend than on with a complex non linear relationship. 

Carbosilane dendrimers are kinetically and thermodynamically very stable and their structures can be easily modified for the required application. In view of the emerging importance of dendrim-ers as a new class of materials and the versatility of carboranes in applications, we were interested in functionalizing the periphery of dendrimers with carborane clusters. Our aim was to generate new star-shaped macromolecules using carbosilanes as an inert scaffold in which carborane derivatives were attached on the periphery. 

The major advantage of our approach is that the desirable features of inorganics and organics such as high thermal and oxidative stability and processability are incorporated into the same polymeric chain. The siloxane units provide thermal and chain flexibility to polymeric materials. Siloxane-acetylenic polymers have also been made but lack the thermal and oxidative stability that the carborane units possess. The chemistry involved in synthesizing poly(siloxane) and poly(carborane-siloxane) has been modified to accommodate the inclusion of an acetylenic unit in the backbone. The novel linear... 

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