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. 2019 Sep 22;11(10):1543. doi: 10.3390/polym11101543

Figure 1.

Figure 1

Elementary reaction mechanism for urethane bond formation. The alcohol excess mechanism (top) involves a hydrogen-bonded alcohol associate as the reactant, while the isocyanate excess mechanism (bottom) starts with dipole-dipole stabilized intermolecular isocyanate dimer. In the present study R = Pr and Ar = Ph.