Selectivity of Isophorone Diisocyanate in the Urethane Reaction Influence of Temperature, Catalysis, and Reaction Partners

By R. Lomölder, F. Plogmann, P. Speier

Isophorone diisocyanate (IPDI) (Figure 1) is the lead-ing cycloaliphatic diisocyanate worldwide for the preparation of light-stable, urethane-modified coating resins such as PU dispersions, urethane alkyds, radiation-curable urethane acrylates, and moisture-cure isocyanate prepolymers.

One of the main reasons for the expanding use of this product in numerous applications, besides the very broad compatibility with co-reactants and solvents, is the unequal reactivity of the primary aliphatic and the secondary cycloaliphatic isocyanate groups of IPDI, which leads to low viscosity products with a narrow molecular weight distribution and a low free monomeric diisocyanate content.¹

This reactivity difference has been the subject of investigation in the past.2-8 As a result of various assumptions, stoichiometry, reaction partners, experimental methods and interpretations, the reactivity difference between the NCO groups has been reported to be in the range of 0.2:1 to 12:1.