Mechanism addition-elimination, and

Wicks has reviewed the various reaction mechanisms with blocked isocyanates. There are two general mechanisms (addition-elimination and elimination-addition) by which the blocked isocyanate reacts with a hydroxyl compound (Figure 6.2.11, A and B). It is possible that a particular type of blocked isocyanate can function by either mechanism, depending on such factors as the type of blocking group, type of hydroxyl compound, temperature, and the polarity of the solvent. Tin catalysts such as DBTDL are often included in such formulations, but higher concentrations are required than in reactions with isocyanates and the role of the catalyst is not always well defined. 

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