Explain the preparation of silicones.

Explanation

Generally silicones are prepared by the hydrolysis of dialkyldichlorosilanes `(R_(2)SiCl_(2))` or diaryldichlorosilanes `Ar_(2)SiCl_(2)`, which are prepared by passing vapours of RCl or ArCl over silicon at 570 K with copper as a catalyst.
`2RCl+Si overset(Cu//570K)to R_(2)SiCl_(2)`
The hydrolysis of dialkylchloro silanes `R_(2)SiCl_(2)` yields to a straight chain polymer which grown from both the sides.
`Cl-underset(R)underset(|)overset(R)overset(|)Si-Cl underset(-2HCl)overset(+2H_(2)O)toHO-underset(R)underset(|)overset(R)overset(|)Si-OH`
`HO-underset(R)underset(|)overset(R)overset(|)Si-OH+HO-underset(R)underset(|)overset(R)overset(|)Si-OH underset(-H_(2)O)toHO-underset(R)underset(|)overset(R)overset(|)Si-O-underset(R)underset(|)overset(R)overset(|)Si-OH+HO-underset(R)underset(|)overset(R)overset(|)Si-OH`
`underset(-H_(2)O) to HO-underset(R)underset(|)overset(R)overset(|)Si-O-underset(R)underset(|)overset(R)overset(|)Si-OH-underset(R)underset(|)overset(R)overset(|)Si-OH underset(-H_(2)O) to Etc`
The hydrolysis of monoalkylchloro silanes `RSiCl_(3)` yields to a very complex cross linked polymer. Linear silicones can be converted into cyclic or ring silicones when water molecules is removed from the terminal -OH groups.