Editing Silicone (section)

== Synthesis ==
Most common are materials based on [[polydimethylsiloxane]], which is derived by [[hydrolysis]] of [[dimethyldichlorosilane]].  This dichloride reacts with water as follows:

<math chem display=block>n\ \ce{Si(CH3)2Cl2} + n\ \ce{H2O -> [Si(CH3)2O]}_n + 2n\ \ce{HCl}</math>

The polymerization typically produces linear chains capped with {{chem2|Si\sCl}} or {{chem2|Si\sOH}} ([[silanol]]) groups.  Under different conditions, the polymer is a cyclic, not a chain.<ref name=Ullmann/>

For consumer applications such as caulks, silyl [[acetate]]s are used instead of silyl chlorides.  The hydrolysis of the acetates produces the less dangerous [[acetic acid]] (the acid found in [[vinegar]]) as the reaction product of a much slower curing process. This chemistry is used in many consumer applications, such as silicone [[caulk]] and [[adhesive]]s.

<math chem display=block>n\ \ce{Si(CH3)2(CH3COO)2} + n\ \ce{H2O -> [Si(CH3)2O]}_n + 2n\ \ce{CH3COOH}</math>

[[Branching (polymer chemistry)|Branches]] or crosslinks in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyl trichlorosilane and [[methyltrimethoxysilane]]. Ideally, each molecule of such a compound becomes a branch point. This process can be used to produce hard silicone resins. Similarly, precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.