Investigating oxazine exchange reactions for thermally curable naphthoxazine synthesis

A compound, namely 4-(1H-naphtho[1,2-e][1,3]oxazin-2(3H)-yl)phenol, bearing a phenolic –OH group, was successfully synthesized. This compound was then subjected to Mannich reactions with primary amine compounds and paraformaldehyde, in a molar ratio of 1:1:2, respectively. Interestingly, these Mannich reactions yielded three distinct thermally polymerizable naphthoxazines, over unprecedented amine exchange reactions with high yields. The structures of the resulting exchange products were thoroughly characterized using analytical techniques, such as NMR, GC–MS, and FT-IR spectroscopy. Additionally, a model reaction was conducted to provide better insights into these exchange reactions. Furthermore, the ring-opening polymerization behavior of the synthesized naphthoxazines was investigated using a differential scanning calorimeter (DSC).