Reprocessable polybenzoxazine thermosets crosslinked by mussel-inspired catechol-Fe3+ coordination bonds

The traditional thermosets cannot be reprocessed, which causes serious environmental pollution and resource waste. The catechol-Fe3+ coordination bonds existing in marine mussel byssal cuticle provide a reversible crosslinking structure for reprocessable thermosets. A reprocessable polybenzoxazine thermoset (PBOZ-dopa(45-)Fe(3+)) by catechol-Fe3+ coordination bonds was synthesized successfully based on mussel-inspired chemistry and benzoxazine chemistry. Firstly, benzoxazine monomers containing carboxyl groups were synthesized. Secondly, polybenzoxazine with carboxyl groups was obtained through thermal ring-opening polymerization. And then catechol groups were grafted onto the pendant groups of polybenzoxazine. Finally, the reprocessable polybenzoxazine was obtained by catechol groups coordinating with Fe3+. The structure of polybenzoxazine was characterized by NMR, FTIR and SEC measurements. The formation of reversible crosslinked network composed of catechol-Fe3+ coordination bonds is confirmed by UV-Vis absorbances, system color changes, and dissolution states in methanol solutions of different pH. Reprocessing experiments indicate that the reversible catechol-Fe 3+ coordination bonds endow remarkable reprocessability of cured resin. Dynamic mechanical measurements and thermogravimetric measurements show that the PBOZ-dopa(45-)Fe(3+) can still maintain excellent thermal properties. Cross-linking by catechol-Fe3+ coordination bonds provides a new way for the preparation of reprocessable thermosets.