condensationcure

Condensation cure, or condensation-cure, is a curing mechanism used by certain polymers, notably silicone sealants and elastomers, in which crosslinking occurs via a condensation reaction that releases a small byproduct such as water or an alcohol. This mechanism contrasts with addition-cure systems that crosslink without byproducts.

In condensation-cure silicones, functional groups on the polymer chains react in the presence of moisture and a catalyst, often tin-based, to form siloxane networks. The byproduct is water or a low-molecular-weight alcohol. Acetoxy-type formulations release acetic acid, which can have an odor and potential corrosive effect on some metals, while alkoxy formulations release alcohol and are generally less odorous.

Curing is typically moisture dependent and occurs at ambient temperatures, but the rate depends on humidity, temperature, and substrate. Because water or alcohol is produced, these systems can exhibit slower cure, potential surface inhibition, and interaction with certain metals or moisture-sensitive substrates. The acidity and odor of acetoxy types can be drawbacks in enclosed spaces, and some formulations may require surface preparation or primers for optimal adhesion.

Applications include construction sealants for glazing and weatherproofing, industrial adhesives, and other sealants where moisture exposure is acceptable. They offer good adhesion to glass and many metals, flexible elastomeric properties, and resistance to weathering. However, they may require careful substrate compatibility considerations and are sometimes slower to cure than alternative systems.

See also: silicone sealant, condensation cure versus addition cure, neutral cure, acetoxy cure, alkoxy cure.