- These are organosilicon polymers containing Si-O-Si linkages.
- These are formed by the hydrolysis of alkyl or aryl substituted chlorosilanes and their subsequent polymerization.
- The alkyl or aryl substituted chlorosilanes are prepared by the reaction of Grignard reagent and silicon tetrachloride.
RMgCl + SiCl4 → R−SiCl3 + MgCl2
2RMgCl + SiCl4 → R2SiCl2 + 2MgCl2
3RMgCl + SiCl4 → R3SiCl + 3MgCl2
- Hydrolysis of substituted chlorosilanes yields corresponding silanols, which undergo polymerization.
- R3SiCl on hydrolysis forms only a dimer.
R3SiOH + HOSiR3 → R3Si − O − SiR3 + H2O
Silicones are of the following types:
- Linear silicones
- Cyclic silicones
- Cross linked silicones
- The lower silicones are oily liquids but higher members containing long chains or ring structures are waxy and rubber-like solids.
- Silicones are stable towards heat.
- Chemical reagents have no action on silicones.
- These are non-toxic.
- Viscosity of silicone oils remains the same at different temperatures.
- Silicones are good electrical insulators.
- Silicones are water repellents.
- Used for high temperature oil baths, high vacuum pumps etc as they are highly stable and non-volatile.
- Used for low-temperature lubrication.
- Used in making water-proof cloth and paper as they are water repellent.
- Used in insulating electric motors.