Silicon carbide from polycarbosilane polymers

Other organosilicon polymer precursors for ceramics have either been prepared or improved by means of transition metal complex-catalyzed chemistry. For instance, the Nicalon silicon carbide-based ceramic fibers are fabricated from a polycarbosilane that is produced by thermal rearrangement of poly(dimethylsilylene) [18]. The CH3(H)SiCH2 group is the major constituent of this polycarbosilane. 

The discovery by Yajima that polysilanes could be pyrolyzed to silicon carbide was mentioned in the introduction.7 In this process, either (Me2Si) or the cyclic oligomer (Me2Si)6 are synthesized from Me2SiCl2 and are then heated to near 450 °C (Scheme 5.10). This discovery has been commercialized by the Nippon Carbon Co. for the production of NICALON silicon carbide fibers. In this process, methylene groups become inserted into many of the Si-Si bonds to give a polycarbosilane polymer with the idealized 5.14. 

Idesaki, A., Narisawa, M., Okamura, K., Sugimoto, M., Morita, Y., Seguchi, T., Itoh, M., Application of electron beam curing for silicon carbide fiber synthesis from blend polymer of polycarbosilane and polyvinylsilane. Radiation Physics and Chemistry 2001,60(4-5), 483-487. 

Nonoxides can be formed from polymeric precursors that are already mixed in the right proportion on an atomic scale. The atoms in silicon carbide are bonded with covalent bonds and are not mobile. Similar to most other carbides and nitrides SiC is difficult to sinter and so has slow solid state reactions even at high temperatures. A good precursor for solid state formation of SiC is the polymer polycarbosilane, which is made at 450°C from polysilanes formed from dimethyl-dichlorosilane and sodium ... 

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