text: The Stöber process is a well-studied example of polymerization of an alkoxide, specifically TEOS. The chemical formula for TEOS is given by Si(OCH), or Si(OR), where the alkyl group R = CH. Alkoxides are ideal chemical precursors for sol–gel synthesis because they react readily with water. The reaction is called hydrolysis, because a hydroxyl ion becomes attached to the silicon atom as follows:
  :Si(OR) + HO → HO−Si(OR) + R−OH
  Depending on the amount of water and catalyst present, hydrolysis may proceed to completion to silica:
  :Si(OR) + 2 HO → SiO + 4 R−OH
  Complete hydrolysis often requires an excess of water and/or the use of a hydrolysis catalyst such as acetic acid or hydrochloric acid. Intermediate species including [(OR)−Si−(OH)] or [(OR)−Si−(OH)] may result as products of partial hydrolysis reactions. Early intermediates result from two partially hydrolyzed monomers linked with a siloxane [Si−O−Si] bond:
  :(OR)−Si−OH + HO−Si−(OR) → [(OR)Si−O−Si(OR)] + H−O−H
  or
  :(OR)−Si−OR + HO−Si−(OR) → [(OR)Si−O−Si(OR)] + R−OH
  Thus, polymerization is associated with the formation of a 1-, 2-, or 3-dimensional network of siloxane [Si−O−Si] bonds accompanied by the production of H−O−H and R−O−H species.
  By definition, condensation liberates a small molecule, such as water or alcohol. This type of reaction can continue to build larger and larger silicon-containing molecules by the process of polymerization. Thus, a polymer is a huge molecule (or macromolecule) formed from hundreds or thousands of units called monomers. The number of bonds that a monomer can form is called its functionality. Polymerization of silicon alkoxide, for instance, can lead to complex branching of the polymer, because a fully hydrolyzed monomer Si(OH) is tetrafunctional (can branch or bond in 4 different directions). Alternatively, under certain conditions (e.g., low water concentration) fewer than 4 of the OR or OH groups (ligands) will be capable of condensation, so relatively little branching will occur. The mechanisms of hydrolysis and condensation, and the factors that bias the structure toward linear or branched structures are the most critical issues of sol–gel science and technology. This reaction is favored in both basic and acidic conditions.