Effect of molecular backbone structure on vapor phase coupling reaction between diiso(thio)cyanates with diamines, diols, and dithiols

Abstract

Gas phase vacuum deposition processes such as chemical vapor deposition or molecular layer deposition can be used to deposit conformal thin films of organic polymers. Urea and urethane are typical products in such vacuum thin film deposition methods that are obtained from spontaneous, catalyst- and solvent-free reactions between isocyanates/isothiocyanates and amines/diols/thiols. In this work, the thermochemistry of the urea/urethane coupling reactions between homobifunctional reactants is analyzed using double-hybrid density functional theory calculations. The reactant pairs are chosen such that the molecular backbone structures are either aromatic (-C6H4-) or aliphatic (-(CH2)(4)-) in both reactants. It is observed that the activation energies of the reactions can be correlated with the basicity of the amines/alcohol/thiol species. Furthermore, since the chemical properties are dependent on the structure of the molecular backbone, the molecular reactivity of the aliphatic reactant pairs are suggested to be higher than aromatic ones.