Synthesis of 9,9‐bis(4‐aminophenyl)fluorene‐based benzoxazine and properties of its high‐performance thermoset

A benzoxazine ( P‐bapf ) based on 9,9‐bis(4‐aminophenyl)fluorene (BAPF), phenol, and formaldehyde was successfully prepared using two‐pot and one‐pot procedures. In the two‐pot approach, BAPF initially reacted with 2‐hydroxybenzaldehyde, leading to 9,9‐bis(4‐(2‐hydroxybenzylideneimino)phenyl)fluorene. The imine linkages of 9,9‐bis(4‐(2‐hydroxybenzylideneimino)phenyl)fluorene were then reduced by sodium borohydride, forming 9,9‐bis(4‐(2‐hydroxybenzylamino)phenyl)fluorene. Finally, paraformaldehyde was added to induce ring closure condensation, forming benzoxazine ( P‐bapf ). In the one‐pot approach, P‐bapf was obtained directly by reacting BAPF, phenol, and paraformaldehyde in various solvents. Among the solvents, we found that using toluene/ethanol (2/1, v/v) as a solvent leads to the best purity and yield. No gelation was observed in the preparation. The structure of the resulting benzoxazine was confirmed by 1 H, 13 C, 1 H 1 H and 1 H 13 C NMR spectra. P‐bapf exhibits a photoluminescent emission at 395 nm under an excitation of 275 nm. After curing, the resulting P‐bapf thermoset exhibits T g as high as 236 °C, and the T g can be further increased to 260 °C by copolymerization with an equal equivalent of cresol novolac epoxy. The 5% degradation temperature of the P‐bapf thermoset reaches as high as 413 °C (N 2 ) and 431 °C (air). The refractive index at 589 nm is as high as 1.70, demonstrating a high refractive index characteristic of fluorene linkage.