Isocyanates react with compounds that have active hydrogens. For example, in coating applications, isocyanates are typically reacted with polyols to form polyurethanes, or with primary and secondary amines to form polyureas. Catalysis of the polyol/isocyanate reaction, which is often required to develop sufficient cure response, can be achieved with a variety of compounds. The most common catalysts for the polyol/isocyanate reactons include metal salts, organometallic compounds and tertiary amines. Generally speaking, bases, acids and even water can, in some cases, accelerate isocyanate reactions.
Catalyst selection can be a very complicated process, particularly for urethane coating formulations, which contain ingredients that can either accelerate or decelerate the reaction rate by interacting with catalysts or active resins. Among the most common catalyst deactivating components in typical polyurethane formulations are water (hydrolysis), pigment (absorption), solvents (solubility) and acid groups (formation of inactive salts).