Catalyst-free Dynamic Covalent Knoevenagel/Hydrazide Condensa-tion for Polyacylhydrazones and Covalent Adaptable Networks

The rapid advancement of dynamic covalent chemistry (DCvC) has significantly impacted both chemistry and materials science. There is an increasing need for exploring catalyst-free dynamic covalent reactions with large equilibrium con-stant (Keq) ranges to provide new avenues for the tailored design of dynamers. Here, we report a catalyst-free dynamic covalent condensation reaction between Knoevenagel derivatives and hydrazides to generate acylhydrazones. Systematic small-molecule studies validate a significant substituent effect on the Kn reactant, resulting in a wide Keq range covering nearly four orders of magnitude (0.1 ~ 719). The high Keq values (> 500) achieved in polar aprotic solvents enable the catalyst-free synthesis of high-molar-mass (~ 180 kDa) polyacylhydrazones. The retention of by-products during poly-condensation leads to concentration-dependent topology switching between polymeric and macrocyclic acylhydrazones. By leveraging this reaction, we developed a novel covalent adaptable network (CAN) that exhibits remarkable stress re-laxation properties (38 s at 160 °C), facilitating efficient thermal reprocessing while maintaining high mechanical perfor-mance. This condensation reaction enriches the dynamic covalent toolbox and offers a versatile approach for the design and fabrication of dynamers with tailored mechanical and dynamic behavior.