Discuss the preparation and properties of silicones.

(N/A) Silicones are a group of organosilicon polymers,which have $(R_{2}SiO)_{n}$ as a repeating unit. The starting materials for the manufacture of silicones are alkyl or aryl substituted silicon chlorides,$(R_{n}SiCl_{(4-n)})$ where $R$ is an alkyl or aryl group.
Preparation:
$1$. When methyl chloride reacts with silicon in the presence of copper as a catalyst at a temperature of $570 \ K$,various types of methyl-substituted chlorosilanes of formula $(MeSiCl_{3}, Me_{2}SiCl_{2}, Me_{3}SiCl)$ with a small amount of $Me_{4}Si$ are formed.
$2$. Hydrolysis of dimethyl dichlorosilane,$[(CH_{3})_{2}SiCl_{2}]$,followed by condensation polymerization,yields straight-chain polymers.
$3$. The chain length of the polymer can be controlled by adding $(CH_{3})_{3}SiCl$,which blocks the ends.
Properties:
$1$. Silicones are surrounded by non-polar alkyl groups,making them water-repellent in nature.
$2$. They generally have high thermal stability,high dielectric strength,and resistance to oxidation and chemicals.