Shining a new light on the structure of polyurea/polyurethane materials

Polyurea and polyurethane containing urea bonds are widely used in the preparation of coatings, foams, and micro- and nanocapsules. The molecular structures of such materials are typically difficult to characterize quantitatively due to their poor solubility and because mixtures with strong acids tend to hydrolyze the polymers. In a mixture of trifluoroacetic acid (TFA) and acetone, a very strong hydrogen bonding occurs between the carbonyl oxygen of acetone and the proton of TFA, which leads to its deshielding. This peculiar mixture of solvent was used for the quantitative characterization of polyurethane/urea coatings, microcapsules, and nanocapsules by NMR spectroscopy. By using aromatic and aliphatic diisocyanates, diamines, and diols, the extent of urea groups, and hence hydrolyzed isocyanates, in the polymer can be determined. This method is shining light on materials that were not yet quantitatively characterized such as polyurea nanocapsules prepared by interfacial polymerization in miniemulsion.