Iminoboronate-Based Covalent Adaptable Networks with Rapid Exchange Kinetics and Hydrolysis Stability

Abstract

Boronic ester bonds have been widely applied in covalent adaptable networks (CANs) owing to their broadly tunable dynamics. However, the design of boronic ester bonds has long been plagued by an inherent trade-off between dynamics and hydrolytic stability: accelerating the exchange rate seems to inevitably compromise resistance to hydrolysis. To break this deadlock, we introduce an ortho-imine to the cyclic boronic ester, developing an “iminoboronate” that features rapid exchange at low temperatures together with enhanced hydrolytic stability. Utilizing the imine as an endogenous base catalyst, the transesterification rate is increased by six orders of magnitude, far surpassing the dynamic range achievable with existing boronic esters. The ortho‑imine coordination also reduces the hydrolysis equilibrium constant by a factor of 32 compared to conventional cyclic boronic esters. Moreover, as difunctional crosslinkers, the iminoboronates enable bulk CANs with markedly improved toughness (84.5 vs. 6.2 MJ·m−3), reprocessability, humidity resistance, and self‑healing performance compared to the control network crosslinked via non-coordinated boronic ester bonds. This work fills the mechanistic gap in iminoboronate chemistry while offering a promising strategy for designing high-performance CANs.