Vanillin-Derived Polybisbenzoxazine: Tailoring Mechanical Performance and Circularity via Dynamic Imine Chemistry

Abstract Traditional petroleum-based thermosetting polybenzoxazines face significant environmental challenges due to their nonrecyclability and dependence on fossil resources. In this study, a series of fully biobased, imine-cross-linked polybisbenzoxazine networks (VD-Cx) were successfully synthesized using a vanillin-derived dialdehyde (VD) and various biobased diamines with different alkyl chain lengths (C4, C6, C10, and Priamine 1074). The chemical structures and curing behavior were confirmed via FT-IR, demonstrating the successful formation of imine linkages and subsequent thermal ring-opening polymerization of the oxazine rings. By adjusting the carbon chain length of the diamines, the properties of the VD-Cx networks could be precisely tuned: VD-C4 exhibited high rigidity and strength (65.2 MPa), while VD-1074 showed excellent flexibility with an elongation at break of 164.5%. Due to the dynamic nature of the imine bonds, the networks displayed rapid stress relaxation and a topological freezing transition temperature (Tv) ranging from 63.6 to 127.3 °C. The materials demonstrated excellent thermal stability (Td5% > 240 °C), robust reprocessability (with VD-C10 retaining 89.6% of its strength after two cycles), and triple-shape-memory behavior. Furthermore, the VD-Cx networks could be completely degraded in an acidic HCl/THF solution, offering a pathway for chemical recycling. This work provides a promising strategy for developing high-performance, multifunctional, and potentially circular biobased thermosets.