Cure mechanism, urea-urethane

The presence of water will lead to the formation of ureas and evolve CO2 as shown in Fig. 5. This mechanism is thought to proceed through the formation of an unstable intermediate, carbamic acid, which then decomposes to give CO2 and an aromatic amine. The amine will then react further with another isocyanate to give a urea linkage. All common moisture-cured urethanes give off CO2 upon curing, which can pose problems... 

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