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 1H, 13C, 1H1H and 1H13C 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 Tg as high as 236 °C, and the Tg 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 (N2) 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. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012