Cost-Effective Method for the Synthesis of Polysilanes
Publication Date: 2007-May-23
The IP.com Prior Art Database
Described herein are non-limiting embodiments of a method for the synthesis of polysilanes from a mixture of chloropolysilanes.
This mixture is a byproduct of silane manufacturing and can therefore be obtained at low cost. What is proposed here is to reduce the whole mixture by Iithium aluminum hydride or sodium borohydride to form a mixture of polysilanes and to separate them by trapping them at appropriate temperature. Alternatively, to separate the lightest ones (Si2CI6 and Si3CI8) from the heaviest ones for the sake of saving the reductant, to form preferentially disilane and trisilane, which are of commercial interest.
BRIEF DESCRIPTION OF THE PRIOR ART
Silane, disilane, trisilane, tetrasilane, and a mixture of pentasilane and hexasilane were prepared by the reaction of aqueous acids with magnesium silicide produced by the reduction of silicon oxide with magnesium. Even though it was found that matters were improved by adding the silicide slowly to the acid instead of the other way around, and by using dilute phosphoric acid instead of hydrochloric acid, only one fourth of the silicon in the silicide appeared as silanes; of this fourth, 40% was silane, 30% disilane, 15%trisilane, 10% tetrasilane, and 5% higher silanes. The rest of the silicon remained in the bath probably consisting of siloxanes or polysiloxanes. A later chromatography study of the volatile products showed that 21 products were actually present. Since Si-H bond is very sensitive to moisture or water, yield could have been obtained using moisture-free system: In another instance, a solution of ammonium chloride solution in liquid ammonia as the acid was used.
A second method involves the reduction of the corresponding chlorosilanes by lithium aluminum hydride or similar reductants. For example, the reduction of tetrachlorosilane by LiAIH4 in ether solution leads to high yields of silane. This method can be used for substituting halogens or even alkoxides bonded to silicon by hydrogen. This makes the hydrogenation by LiAJH4 the most convenient method to prepare silanes.
A third method to synthesize polysilane consists in introducing silane in a glow discharge: Disilane and trisilane can be obtained but only in very low yield.
PROBLEM SOLVED BY THE INVENTION
Disilane and trisilane are of growing commercial interest as processes have been recently developed to form polycrystalline silicon, silicon nitride, silicon oxide, ternary compounds, and silicides but it is not available at rea...