The hydrogen bonding of polybenzoxazines was investigated using a number of oligomeric model systems using advanced solid-state NMR techniques. Both intermolecular and intramolecular hydrogen-bonding interactions were probed using dipolar-recoupling, multiple quantum coherence and fast-MAS. Insight into the supramolecular structure was gained exploiting the proximity dependent nature of the nuclear dipole-dipole interaction via 1H–1H homonuclear and 1H–13C heteronuclear 2D NMR methods. The supramolecular structure of the model dimers was shown to be influenced by both ring and amine-substituents, with steric hindrance found to strongly affect hydrogen bond strength. Such an influence of the amine-substituent was also demonstrated for the model trimers, however with more complex supramolecular structures suggested. All model systems showed a general propensity to form strong N••H-O and O••H-O hydrogen bonds, with evidence of polymorphism seen for many systems. Interpretation of experimental results were complemented by ab-initio electronic structure methods combined with chemical shift calculation, allowing possible geometries to be tested and refined.
