Biobased N,O-acetal covalent adaptable networks with enhanced thermomechanical properties and flame-retardancy

Two fluorinated N,O–acetal CANs containing a high density of aromatic groups, and granted with flame retardancy ability, are reported. N,O–DFDA was prepared from difurfurylamine (DFDA), a bio–based diamine, while N,O–MXDA was synthesized from petroleum-based MXDA. The networks were prepared by reductive amination of hydroxymethylfurfural (HMF) with either of these two diamines, followed by condensation of the resulting secondary diamine with trifluoroacetaldehyde methyl hemiacetal. These materials exhibited high gel content (93–97 %) and fast covalent exchange kinetics (short relaxation times: 170–300 s at 140 °C). They also showed valuable thermal properties with 50 % of char yield and a very low heat release (5–6 kJ/g). N,O–DFDA was reprocessable under relatively mild conditions (1 h, 140 °C, and 3 tons) without any major changes in its properties after 3 reprocessing cycles. Closed-loop chemical recycling of the material was performed by complete depolymerization in methanol at 120 °C and repolymerization. Finally, NO–DFDA presented a strong hydrolytic stability in neutral and basic media at room temperature and at 100 °C.