Tuning Acylhydrazone Exchange Dynamics via Substituent Effects for Reprocessable and High-Resolution 3D Printable CANs

Acylhydrazone-based Covalent Adaptable Networks (CANs) are attractive candidates for recyclable thermosets due to their strong hydrogen bonding and excellent creep resistance. However, their slow exchange kinetics under catalyst-free conditions severely restricts reprocessability and advanced manufacturing potential. Herein, a substituent-guided molecular design strategy is proposed to tune the acylhydrazone exchange dynamics through the electronic effects of aromatic substituents. This approach enables programmable control over viscoelastic behavior, achieving a unique balance between rapid stress relaxation (τ = 187 s at 100 °C) and high creep resistance (onset up to 130 °C). The nitro-functionalized network exhibits strong intrinsic UV absorption, enabling dye-free, high-resolution DLP 3D printing (600 μm features) with excellent printing fidelity. Moreover, the printed materials display efficient reprocessability at 180 °C and thermal self-healing at 130 °C with minimal loss of mechanical strength. This catalyst-free and generalizable design provides deeper insight into substituent-driven dynamic control and offers a practical pathway for recyclable, precision-manufacturable thermoset systems relevant to sustainable polymer engineering.