Question
How are silicones prepared? Write their properties.
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Answer
$i.$ Preparation of silicones:
$a.$ Alkyl or aryl substituted silicon chlorides having general formula $R_nSiCl_{(4-n)} (R =$ alkyl or aryl group$)$ are used as the starting materials for manufacture of silicones.
$b.$ When methyl chloride reacts with silicon in the presence of copper catalyst at a temperature $573 K,$ various types of methyl substituted chlorosilane of formula $MeSiCl_3, Me_2SiCl_2, Me_3SiCl$ with small amounts of $Me_4Si$ are formed.
$c.$ Hydrolysis of dimethyldichlorosilane, $(CH_3)_2SiCl_2$ followed by condensation polymerisation yields straight chain silicone polymers.
$d.$ The chain length of polymer can be controlled by adding $(CH_3)_3SiCl$ at the end.
$ii.$ Properties:
Silicones are water repellent.
They have high thermal stability.
They are good electrical insulators.
They are resistant to oxidation and chemicals.
$a.$ Alkyl or aryl substituted silicon chlorides having general formula $R_nSiCl_{(4-n)} (R =$ alkyl or aryl group$)$ are used as the starting materials for manufacture of silicones.
$b.$ When methyl chloride reacts with silicon in the presence of copper catalyst at a temperature $573 K,$ various types of methyl substituted chlorosilane of formula $MeSiCl_3, Me_2SiCl_2, Me_3SiCl$ with small amounts of $Me_4Si$ are formed.
$c.$ Hydrolysis of dimethyldichlorosilane, $(CH_3)_2SiCl_2$ followed by condensation polymerisation yields straight chain silicone polymers.
$d.$ The chain length of polymer can be controlled by adding $(CH_3)_3SiCl$ at the end.
$ii.$ Properties:
Silicones are water repellent.
They have high thermal stability.
They are good electrical insulators.
They are resistant to oxidation and chemicals.
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