R R Si OH R R Etc -H O -H O The hydrolysis of monoalkylchloro silanes RSiCl yields to a very complex cross linked polymer.. Linear silicones can be converted into cyclic or ring silicones when water molecules is removed from the terminal –OH groups. Si Me Me Si Me Me Si Me Me Si Me Me Si Me Me Si Me Me Si Me Me Si R Si R Si R Si R Si R Types of silicones: (i) Linear silicones: They are obtained by the hydrolysis and subsequent condensation of dialkyl or diaryl silicon chlorides. - - - - a) Silicone rubbers: These silicones are bridged together by methylene or similar groups b) Silicone resins: They are obtained by blending silicones with organic resins such as acrylic esters.
(ii) Cyclic silicones These are obtained by the hydrolysis of R SiCl . (iii) Cross linked silicones They are obtained by hydrolysis of RSiCl Properties The extent of cross linking and nature of alkyl group determine the nature of polymer. They range from oily liquids to rubber like solids. All silicones are water repellent.
This property arises due to the presence of organic side groups that surrounds the silicon which makes the molecule looks like an alkane. They are also thermal and electrical insulators. Chemically they are inert. Lower silicones are oily liquids whereas higher silicones with long chain structure are waxy solids.
The viscosity of silicon oil remains constant and doesn’t change with temperature and they don't thicken during winter Uses: . Silicones are used for low temperature lubrication and in vacuum pumps, high temperature oil baths etc... . They are used for making water proofing clothes .
They are used as insulating material in electrical motor and other appliances . They are mixed with paints and enamels to make them resistant towards high temperature, sunlight, dampness and chemicals. . .
Silicates The mineral which contains silicon and oxygen in tetrahedral [SiO ] - units linked together in different patterns are called silicates. Nearly % of the