Jap

In contrast to the sol-gel and other processing methods, synthetic organometallic polymers obtained from well-defined building units can be used directly in applications such as coatings, fibers, or bulk shapes and subsequently pyrolyzed to the desired ceramic. The repetition and/or combination of modular units shown in Scheme 22 allows the fabrication of different organometallic precursors. Polycarbosilanes used as precursors to silicon carbide (SiC) can be synthesized with different alkyl groups according to the following equation [333]:

n(CH3)2SiCl2 + 2 nNa

Scheme 22.

Furthermore, new molecular precursors such as hydri-dopolycarbosilane (Scheme 24), which is a single-component liquid source, have been developed to obtain high-purity SiC [524].

Scheme 24.

Polysilazanes are prepared in a straightforward reaction of (CH3)„SiCl4-„ with NH2(H, R), whereby HCl is eliminated and a low-molecular compound is formed that can be polymerized by employing dehydrocoupling catalysts like KH, Ru3(CO)12, etc. [525] (Scheme 25). The synthesis route

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