Silicones

Silicones are synthetic organosilicon polymers containing repeated R₂SiO units held by Si-O-Si linkages.

These compounds have general formula (R₂SiO)_n where R=methyl or aryl group.

Preparation

When methyl chloride reacts with silicon in the presence of copper as a catalyst at 570 K , various types of methyl substituted chlorosilanes of formula CH₃SiCl₃ , (CH₃)₂SiCl_2, (CH₃)₃SiCl along with small amount of (CH₃)₄Si are formed.

Hydrolysis of dichlorodimethylsilanes followed by polymerization yields chain polymers.

Properties

1) Silicones made up of short chain molecules are oily liquid, silicones with medium chains behave as viscous oils, jellies and greases, those with very long chains behave as rubbery elastomers and resins.

2) They are chemically inert i.e. resistant to oxidation , thermal decomposition or to attack by organic reagents.

3) Silicones being surrounded by non-polar alkyl group are water repelling in nature.

4) They are heat resistant and have high dielectric strength i.e. have good electrical insulating properties.

Uses

1) For making water proof papers , wool , textile , wood by coating them with a thin film of silicone.

2) As sealants and electrical insulators.

3) As lubricant at high as well as low temperature since there is little change in their viscosities with temperature.

4) Being biocompatible, they are used in surgical and cosmetic implants.