High-Performance Polybenzoxazine Derived from Polyfunctional Benzoxazine Composed of an Oligonuclear Phenolic Compound Having a 4,4′-Dimethylenebiphenyl Linker

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 degrees 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 degrees C, which is approximately 50 degrees C higher than that of PB-a. Moreover, TGA reveals that the thermal stability of POP-a is also enhanced.