Silicones

Silicones

Silicones are a group of organosilicon polymers, which have (R2SiO) as a repeating unit. The starting materials for the manufacture of silicones are alkyl or aryl substituted silicon chlorides, RnSiCl(4-n)  where R is alkyl or aryl group. When methyl chloride reacts with silicon in the presence of copper as a catalystat a temperature 573 K various types of methyl substituted chlorosilane of formula MeSiCl3, Me2SiCl2, Me3SiCl with small amount of Me4Si are formed. Hydrolysis of dimethyl-dichlorosilane, (CH3)2SiCl2 followed by condensation polymerization yields straight chain polymers.
Silicones

The chain length of the polymer can be controlled by adding (CH3)3SiCl which blocks the ends as shown below:
Silicones, Silicone

Uses

Silicones being surrounded by non-polar alkyl groups are water repelling in nature. They have in general high thermal stability, high dielectric strength and resistance to oxidation and chemicals. They have wide applications. They are used as sealant, greases, and electrical insulators and for water proofing of fabrics. Being biocompatible they are also used in surgical and cosmetic plants.

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