Silicones

Silicones

Silicones are organosilicon polymers built from a repeating $(R_2SiO)_n$ unit, where R is an alkyl or aryl group. They are manufactured starting from alkyl- or aryl-substituted chlorosilanes, $R_nSiCl_{(4-n)}$.

Reacting methyl chloride with silicon in the presence of copper powder as catalyst, at about 573 K, gives a mixture of substituted chlorosilanes — mainly $MeSiCl_3$, $Me_2SiCl_2$ and $Me_3SiCl$, plus a small amount of $Me_4Si$. Hydrolysis of dimethyldichlorosilane, $(CH_3)_2SiCl_2$, followed by condensation polymerisation, yields straight-chain silicone polymers. The chain length can be controlled by adding $(CH_3)_3SiCl$, which reacts at the ends of a growing chain and "caps" it, blocking further growth. …