Reaction of Isocyanates with Urethanes

Urethane groups may be considered hydrogen active compounds, due to the hydrogen atom linked to the nitrogen atom. By the reaction of an isocyanate with an urethane group an allophanate is formed [1, 3, 6-18, 21, 23-25]  

Due to the electron withdrawing effect of the carbonyl groups, the urethane group has a much lower reactivity than the aminic -N-H groups and in order to promote the allophanate formation higher temperatures are necessary greater than 110 °C. It is important to mention that the allophanate formation is a reversible reaction. 

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This section of the chapter will present the basic reactions found in the chemistry of polyurethane compounds, such as the reaction of isocyanates with polyols, water, and amines. The reactions of isocyanates with urethanes, ureas, and amides are also of significant importance in poljrurethane chemistry as they will lead to an increase in materials choice. 

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