A novel polyfunctional benzoxazine monomer, OP‐a, is synthesized from aniline, formaldehyde, and an oligonuclear phenolic compound (OP) with a 4,4′‐dimethylenebiphenyl group as the phenol linker. After thermal curing of OP‐a up to 240 °C, a brown‐colored, transparent polybenzoxazine (POP‐a) film is obtained. The mechanical and thermal properties of the POP‐a film are investigated by tensile test, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The POP‐a film is extremely tough compared with a typical polybenzoxazine (PB‐a) film. The elongation at break of the POP‐a film is 7.6%, which is surprisingly large for the highly cross‐linked thermoset. The high cross‐link density is suggested from the very high storage modulus (over 1 GPa) above the glass transition temperature (T
g) observed by DMA. The T
g of POP‐a is also improved significantly to T
g = 223 °C, which is approximately 50 °C higher than that of PB‐a. Moreover, TGA reveals that the thermal stability of POP‐a is also enhanced.
Front Cover: In article https://doi.org/10.1002/macp.201800317, Takehiro Kawauchi, Tsutomu Takeichi and co‐workers report that a novel polyfunctional benzoxazine yields a remarkably tough polybenzoxazine thermoset film with much improved thermal properties. The benzoxazine is synthesized using an oligonuclear phenolic compound which is commercially available as a curing agent for epoxy resin.
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