Enhanced polybenzoxazine vitrimer molecular network with excellent acid-base and solvent resistance based on cross-linking expansion and through-space conjugation

The participation of dynamic covalent bonds gives Vitrimer materials the ability to "reshape and regenerate". However, the relatively low bond energy of the dynamic covalent bond which vulnerability results in vitrimer materials showing low tolerance during use, thus seriously limits their wide application. In this study, we proposed a molecular network enhancement strategy based on cross-linking expansion and through-space conjugation. Dynamic imine bonds were introduced into the vanillin-based bio-basic benzoxazine resin to achieve the material remodeling and recycling under hot pressing process. Using the through-space conjugation of the benzene ring inside the polybenzoxazine network and the extended cross-linking density of the furan groups, the mesh size inside the material network structure could be reduced by 62.8%, and the mass loss after 24 h of soak in acidic conditions was only 4.85%, and its Young's modulus reached 3049 MPa, and the glass transition temperature was as high as 195.9°C. More importantly, we have proposed the synthesis mechanism of benzoxazine monomer and the differences in the synthesis mechanism of polybenzoxazine under different substituent amine sources. This work provides a reference for the preparation of polymer densification and the development of functional polybenzoxazine materials in the future.