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