Synthesis of itaconimide/nadimide-functionalized benzoxazine monomers: Structural and thermal characterization

A novel series of itaconimide/nadimide-functionalized benzoxazine monomers (I-Bz/N-Bz) from imide-terminated amines, paraformaldehyde and phenol/m-cresol/cardanol/4-(hydroxyphenyl) benzoxazole were synthesized and characterized by FT-IR, 1H and 13C NMR and HRMS analyses. The I-Bzs exhibited lower curing temperatures compared to the N-Bzs, which may be attributable to the presence of the 1,1-disubstituted double bond in itaconimide. The poly(I-Bz)s exhibited higher glass-transition temperatures (210-216 °C) compared to the poly(N-Bz)s (151-178 °C). The itaconimide- and nadimide-functionalized benzoxazines showed comparable thermal stability, but differences in their phenolic structures affected their thermal behavior (char yield and Tmax). The poly(I-Bz)s (19-47%) showed higher char yields compared to the poly(N-Bz)s (18-41%), depending on the backbone structure. The highest lap-shear strength at 200 °C was observed in I-Bz/N-Bz derived from m-cresol.