Storage Life and Reactions of Isocyanates with Themselves—Dimers Uretidinediones

Storage Life and Reactions of Isocyanates with Themselves— Dimers (Uretidinediones) 

Aryl isocyanates readily polymerize in the presence of catalysts into dimers containing 2 moles of the monomeric isocyanate. The reaction and structure is generally considered to be  

These compounds are usually listed as uretidinediones, although the term dimer is frequently applied. The practical consequence of this reaction is that some diisocyanates have a limited storage life, losing activity at different rates. 

Isocyanates, under certain conditions, trimerize into a ring structure 

These two structures may be considered as derivatives of cyanic acid as shown below  

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