Precursors and Industrial Preparation of Polysiloxanes

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Surface Phases on Silicon: Preparation, Structures, and Properties 
Functional silanes of the general formula R_4-nSiX_n, where X is Cl, -OR, -OC(O)R, -NR₂ or other groups that are easily hydrolysed, are the monomers of the polysiloxane synthesis. The most common precursor of polydimethylsiloxane is Me₂SiCl₂ (DDS). 

Since the organosilicon compounds do not appear in nature, all the polysiloxane monomers are obtained on a synthetic route. The natural source of silicon is silica (SiO₂). The synthesis of organosilicon compounds is commonly realized in two steps. Firstly, the silica is reduced to elemental silicon by the carbothermal method. Silicon is then transformed into organosilicon species, most often on one of the following routes:

1.      Reaction of an organic compound with silicon at elevated temperature. This is the industrial route to methylchlorosilanes, called the "Direct Process". 
The reaction mechanism:

xMeCl + Si → Me₃SiCl, Me₂SiCl₂, MeSiCl₃, other products

2.      Chlorination of silicon and a subsequent substitution of some chlorine atoms by organics group with organometallic reagents, such as organolithium compounds, Grigmard reagents, organic zinc compounds and others.

3.      Transformation of organosilicon into  silyl halides and a subsequent addition to multiple bonds in a hydrosilylation process.

Useful for Researchers: Links to Books for Polydimethylsiloxane

Silicon industry is mostly based on dimethyldichlorosilane (DDS), which is exclusively obtained in the Direct Process, involving the reaction of gaseous methyl chloride with a contact mass of silicon containing copper as catalyst in continuously operating reactors equipped with fluidized- or stir-bed at 200-350 °C.


Save hours of researching, check out these reliable good books: 
Silicon in Organic, Organometallic and Polymer Chemistry  
Organosilicon Chemistry VI: From Molecules to Materials (v. 6)



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