Oligomerization
reactions of aliphatic diisocyanates, exclusively involving NCO groups
are discussed. The reactivity and selectivity of these reactions are
dependent on chain length, reaction conditions, and the catalyst employed.
The resulting oligomers (“dimers” and “trimers”)
sometimes deviate considerably from expectation with respect to the
structure and properties. The synthesis and characterization of well-known
derivatives such as uretdiones and isocyanurates are discussed, and
special attention is devoted to the recently developed iminooxadiazinedione
chemistry. Finally, a new class of compounds is introduced, the tricyclic
diiminooxadiazinones.
Since 1961, aliphatic polyisocyanates based on HDI‐biurets are used as light stable hardeners for 2‐K polyurethane coatings. The market introduction of the HDI‐isocyanurates or simply 'trimers' in the early 1980's was driven by their lower viscosity and their better monomer stability. The most recent development in HDI‐polyisocyanate research are the iminooxadiazinediones (asymmetric trimers). In this paper, a new product based on that technology with a very low viscosity (700 mPas@23°C) and a NCO‐functionality of more than 3 is presented. Because of its low viscosity, this hardener can be easily incorporated into aqueous systems and is the solution for high and full solids coatings as well.
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