Silicon-oxygen rings cyclosiloxanes

This later led to the development of the most popular silicone polymers, the polysiloxanes, which, at high molecular weight, exhibit rubbery properties. Such elastomers are generally obtained from a cyclosiloxane monomer by a ring-opening reaction, as shown in Equation (A). Because of the unusual ease of rotation around the silicone-oxygen bond, the polymer chain is much more flexible than carbon-based polymers, so that a semi-liquid material is obtained, even at molecular weights of several hundred thousand. Fine... 

Cyclosiloxanes are inorganic heterocylic rings that contain alternate silicon and oxygen atoms in their cyclic structures [10]. While silicon carries two substituents and is therefore tetracoordinate, oxygen has none and is dicoordinate. In this regard the cyclosiloxanes are similar to cyclophos-phazenes. However, unlike cyclophosphazenes, cyclosiloxanes do not contain a valence unsaturated skeleton. 

Cyclosiloxanes, (RjSiO), are compounds of considerable commercial importance as precursors to silicone polymers. Although a large number of ring sizes can be obtained by the hydrolysis of difunctional silanes, the first members of this series, the cyclodisiloxanes, were not known before the synthesis of tetramesitylcyclodisiloxane [230-233]. This compound is produced nearly quantitatively from tetramesityldisi-lene when the latter is simply exposed to atmospheric oxygen (Eq. 3.90) ... 

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