| The goal of the work described in this dissertation was to develop new processable molecular and polymeric precursors to boron carbide solid state materials that will allow the formation of these technologically important materials in processed forms such as fibers, films and nanostructures. The initial phase of this work required the development of new methods for the formation of new types of organodecaboranes that would serve as the key components of the new precursors. This research resulted in the discovery that certain early metal, Cp2Ti(CO)2 and lanthanide complexes would catalyze the hydroboration of olefins to produce 6-R-B10H 13 species in high yields and selectivity.; The catalysts also proved active for nonconjugated diolefins, with the reaction of decaborane and 1,5-hexadiene yielding, depending on the reaction conditions, hydroboration, 6-CH2=CH(CH2)4-B 10H13, or dihydroboration products, 6,6′-(CH 2)6-(B10H13)2. Likewise, analogous reactions of decaborane with diallylsilanes yielded, 6-[CH 2=CHCH2SiMe2(CH2)3]-B 10H13, and 6,6′-Me2Si((CH 2)3-B10H13)2 and with tetraallylsilane producing the unique cage compound, 6,6′,6″ ,6″′-Si((CH2)3-B 10H13)4.; Products of the titanium catalyzed reactions have been used in the development of or as the precursors themselves to boron carbide and boron-carbide/silicon-carbide composite ceramics. Hexenyldecaborane, 6-CH2=CH(CH2) 4-B10H13, undergoes a Cp2ZrMe 2/B(C6F5)3 catalyzed polymerization to yield a polymer that is soluble and processable well before its decomposition temperature. Polyhexenyldecaborane can be thermally converted to carbon-rich boron carbide at 1250°C with ceramic yields of 65%. A molecular precursor, 6,6′-(CH2)6-(B10H 13)2, has proven to convert to boron-rich boron carbide at 1025°C with ceramic yields of 65%. This molecular precursor has been used in the templated syntheses of various boron carbide nanostructures.; Polymeric precursors for B4C/SiC composites have been developed through the Ind2ZrMe2/B(C6F5) 3 mediated polymerization of 6-[CH2=CHCH2SiMe 2(CH2)3]-B10H13 and copolymerizations of allyltrimethylsilane and hexenyldecaborane. These polymers convert to boron carbide and silicon carbide containing ceramics in varying yields and ratios upon pyrolysis to 1600°C. A molecular precursor, 6,6′-Me 2Si((CH2)3-B10H13) 2, has proven to convert to silicon-containing boron carbide ceramics upon pyrolysis at 1600°C with ceramic yields of 50%. |
