An overview of the chemistry of condensation curing silicone sealants and adhesives

Condensation curing silicone sealants and adhesives are materials that are used to connect substrates to each other in various industries, especially where harsh conditions are limiting the use of organic materials. Chemistry of condensation curing silicones is reviewed in this publication through an historical perspective, which provides an insight into the challenges faced by the early formulators. The impact of the formulation ingredients can be very significant on the uncured, curing and/or cured properties of the material. Their main influence is described with a special focus on the main curing systems, i.e., acetoxy, alkoxy, oxime, amine, acetone, and amide. Cure characteristics are summarized and compared across their chemistries. Alkyl tin carboxylates and alkoxy titanium catalysts are the most used condensation catalysts. They are acting through a different mechanism, which is compared briefly. Typical features and principles about one-part and two-part silicones are described and related to their physicochemical properties. Finally, a brief review of the latest developments and trends is depicted.