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polysilane
Polysilanes are organosilicon compounds with the formula (R2Si)n. They are relatives of traditional organic polymers but their backbones are composed of silicon atoms. They exhibit distinctive optical and electrical properties. They are mainly used industrially as precursors to silicon carbide.
==Synthesis==
The first polysilane, poly(dimethylsilylene), ()''x'', was reported in 1949 by Charles A. Burkhard (1916 - 1991)] of the General Electric Company. It was prepared by heating sodium metal with dimethyldichlorosilane:
:(CH3)2SiCl2 + 2 Na → ()n + 2 NaCl
The modified Wurtz coupling of dichlorosilanes remains a viable and general route to high molecular weight, linear polysilane derivatives. This reaction is conducted at elevated temperature in an inert solvent using a dispersion of the alkali metal. The polymerization stops with the addition of an alcohol. The major limitation with the Wurtz-type polymerization is that the substituents must be able to tolerate the vigorous reaction conditions. The reaction works well for methyl, benzyl, and phenyl substituents.〔 With the rigorous conditions, the yield of the product ranges from a few percent to approximately 50%. Similarly, potassium-graphite (KC8) can be used at much lower temperatures than those required for traditional Wurtz coupling.〔West R. (1986) In: Chandrasekhar, V; Inorganic and Organometallic Polymers; Springer: Berlin, 2005; 3-540-22574-9.〕 This reaction typically produces a trimodal distribution of products: a low molecular weight fraction and two higher molecular weight fractions. The low molecular weight fraction consists of five and six-membered rings, i. e. ()5 and ()6. Formation of these rings competes with the growth of the polymer.〔 Another method for the synthesis of polysilanes is dehydrogenative coupling of silanes.
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