HDI Dimer

Pure HDI molecular weight: 336.39
Molecular formula: C16H24N4O4
CAS number: 23501-81-7
EINECS number: 245-699-5
Structural formula:

There are few varieties of HDI dimer available on the market, and no pure product is available. It is generally a polyisocyanate product mainly composed of HDI dimer (uretdione) with a small amount of trimer. It is mainly used as a curing agent or reactive diluent for light-resistant two-component polyurethane coatings, and as a binder for one-component moisture-curing polyurethane coatings. Due to its low viscosity, it can also be used in solvent-free, high-solids polyurethane coatings and water-based two-component polyurethane coating systems. In two-component systems, it is generally used in combination with other aliphatic polyisocyanates (such as HDI trimer, HDI biuret, IPDI trimer), and the hydroxyl component is preferably acrylate polyol. Bayer’s Desmodur N3400 is a low-viscosity, light yellow liquid, solvent-free (100% solids content), with an NCO content of 21.8% ± 0.7%, free HDI content <0.5%, viscosity (23℃) of 70-250 mPa.s, relative density (20℃) of approximately 1.14, and a flash point of 185℃.