Novel Di-Spiroborate Motif-Enabled Desired Bio-Based Epoxy Covalent Adaptable Networks for Robust, Processable, Recyclable, and Degradable Adhesives

Advanced adhesives design needs to meet multiple requirements of cohesion strength, interfacial activity, re-processability, and degradability, while there exist great challenges to integrate these into single crosslinking network. Here, a novel di-spiroborate structure was designed and synthesized, and then applied to prepare epoxidized soybean oil-based covalent adaptable networks (CANs) adhesives. It was found that the double six-membered ring structure enhanced the rigidity of polymer chains for improved cohesion strength. Moreover, the B-O bond not only optimized interfacial activity via the reactions between electron-deficient boron atoms and the donor groups and nucleophiles of substrate, but also endowed epoxy CANs with re-processability and desired degradability owing to its dynamic property. Given on the effects, the maximum shear strength reached 16.24 MPa, showing an 94.96 % increment compared to the control. Meanwhile, the epoxy CANs adhesives still displayed 85.4 % conservation of lap shear strength after 3 bonding and de-bonding tests. Moreover, the epoxy CANs could be degraded in 1 M HCl/H 2 O solution within 125 min, and the degraded adhesives could rebonding substrate presenting a shear strength of 7.1 MPa. This work provides significant guidance to construct innovative CANs and highlights the development of multi-functional adhesives.