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Discuss preparation and properties of silicones. |
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Answer» SOLUTION :They are a group of organosilicon polymers, which have `(--R_2SiO--)`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 alkyl or aryl group. When methyl chloride reacts with silicon in the presence of copper as a catalyst at a temperature 570K various types of methyl substituted chlorosilane of formula (`MeSiCl_2, MeSiCl_2, Me_3 SiCl_2`) with small amount of `Me_4 Si` are formed. Hydrolysis of dimethyl dichlorosilane, `[(CH_3)_2SiCl_2]`followed by condensation polymerisation yields straight CHAIN polymers.  The chain length of the polymer can be controlled by adding `(CH_3)_3` SiCl which blocks the ends as shown below:  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. |
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