This paper reports the development of the first vitrimer based on polybenzoxazines containing disulfide bonds and cardanol. The synthesis of the monomer was carried out following a sustainable process, without any solvent and purification. The novel polybenzoxazine can be recycled, reshaped and (re)processed, thanks to a fast relaxation process (18 seconds at 120 °C) and low activation energy (64.5 kJ mol⁻¹). Furthermore, the benzoxazine vitrimer shows significant and healable adhesive properties over short times and at low temperatures. These features support it also being considered in additive manufacturing applications, with the possibility of applying 3D printing technology, extending its application to many fields of materials.

This work describes new fully bio-based vitrimers prepared from isosorbide, a renewable sugar-based chemical. Isosorbide was reacted with 4-hydroxypropionic acid, paraformaldehyde, mono-ethanolamine, and/or furfurylamine via consecutive solvent-free Fischer esterification and Mannich-like ring-closure reactions. The two-step synthesis led to the formation of a di-telechelic benzoxazine-terminated isosorbide monomer, containing ester bonds and aliphatic hydroxyl and/or furan groups. The atom economy factor yields 85%. The structural features of the resulting products were substantiated by spectroscopic techniques. The ring-opening polymerization was monitored by rheological and differential scanning calorimetry (DSC) measurements. Very high T_g values afforded by the isosorbide substructure were measured (from 143 to 193 °C), which increase with furan ring content. Internally catalyzed transesterification reactions conferred fast dynamic exchanges (τ* = 300 s at 180 °C). Self-healing and chemical and mechanical recycling were also demonstrated. Finally, the degradability of the sugar-based polybenzoxazine vitrimers was demonstrated as well. The materials were highly stable in pH-neutral water, even at 80 °C for 60 days, but owing to the isosorbide structure, pronounced degradation was observed under acidic or alkaline conditions. In summary, isosorbide is a suitable building block for the design of degradable and 100% recyclable high-T_g polybenzoxazine vitrimers.

With the ongoing efforts to promote the development of bio-based dibenzoxazine thermosets, we explore herein a new strategy aiming at the synthesis of asymmetric dibenzoxazine monomers from naturally occurring phenolic compounds, cardanol and vanillin. By taking advantage of the low reactivity of cardanol, a monosubstituted cardanol-based benzoxazine monomer was prepared and further coupled with vanillin to yield vanillin–cardanol di-benzoxazines. The structural features of the resulting products were substantiated by ¹H NMR and HR-MS. The occurrence of the thermally-induced ring-opening polymerization was monitored by rheological measurements and DSC. At 190 °C the new asymmetric monomers showed a moderate gelation time (8 min) compared to 30–31 min revealed for cardanol-based (di-card) dibenzoxazines. Once polymerized, they exhibited a high T_g (129 °C), while the di-card flew under heating because of its low cross-linking density. Asymmetric monomers also exhibited lower melting temperatures than their symmetrical congeners based on vanillin, which significantly enlarge the processing window between the melting and polymerization temperatures up to 126 °C instead of 7 °C for symmetric vanillin-based dibenzoxazines. Therefore, such a strategy constitutes an efficient and versatile route for an easy elaboration of biobased monocomponent thermosets and can be applied to a wide range of phenolic compounds derived from renewable resources.

This work explores a new strategy, aiming for the synthesis of catalyst-free vitrimers by taking advantage of the abundant number of tertiary amines covalently bound into a polybenzoxazine network. A bio-based monomer was obtained by reacting 4,4-bis(4-hydroxyphenyl)valeric acid, polyethylene glycol, paraformaldehyde and mono-ethanolamine, via consecutive solvent-free Fischer esterification and Mannich-like ring-closure. The two-step reaction led to the formation of quadri-telechelic benzoxazine-terminated polyethylene glycol monomers, containing ester bonds and aliphatic hydroxyl groups. The structural features of the resulting products were substantiated by ¹H NMR, ¹³C NMR, elemental analysis, and FTIR. The occurrence of the thermally induced ring-opening polymerization was monitored by rheological measurements and DSC. At 140 °C, the monomers show a short gelation time (145 seconds). Once polymerized, the polybenzoxazine exhibits a relatively high temperature of α mechanical relaxation (93 °C). Due to the ability of tertiary amines to catalyze transesterification reactions, and to the abundant number of hydroxyl groups, the material enables exchange reactions without the use of an external catalyst. It possesses all the typical characteristics of a vitrimer, such as recycling, reshaping, and self-healing. Short stress-relaxation times were measured (116 s at 170 °C). Finally, the effect of the structural features of the vitrimer was investigated by tuning the crosslinking density of the network and the number of hydroxyl groups, shedding more light on the mechanism of self-catalysis and the range of properties. Therefore, such a strategy constitutes an efficient and versatile route for an easy elaboration of mono-component, catalyst-free, and fast responsive vitrimers.