Dibutyltin dilaurate
For decades the default polyurethane catalyst, dibutyltin dilaurate is now being phased out of many uses in favor of tin-free alternatives.
Dibutyltin dilaurate is an organotin compound: a tin atom bearing two butyl groups and two laurate (dodecanoate) groups. It is a pale liquid or low-melting solid, molecular formula C₃₂H₆₄O₄Sn.
DBTDL catalyzes the isocyanate–hydroxyl (urethane) reaction in 2K polyurethane coatings, sealants, adhesives, foams and RTV silicones. Small amounts shorten gel and dry times substantially.
The tin center coordinates with isocyanate and hydroxyl groups, lowering the energy needed for urethane formation. It is a strong, versatile gel catalyst but is less selective against the isocyanate–water reaction than some alternatives, and residual tin remains in the film.
Organotin compounds are toxic, including to reproduction and aquatic life. Dibutyltin compounds are restricted in many consumer mixtures in the EU under REACH, which has driven the shift to bismuth, zinc and zirconium catalysts.
Bismuth carboxylates such as bismuth neodecanoate, zinc and zirconium catalysts, and some amine catalysts, often in blends tuned for pot life and cure.
Spray polyurea typically does not need a catalyst because amines react with isocyanate very quickly. DBTDL is used mainly in polyol-based polyurethanes.
