Robust Underwater Epoxy Adhesives Enabled by Dynamic Covalent Bond Mediated Two-Stage Curing

Herein, an innovative two-stage curing strategy based on poly(thioctic acid) is proposed for developing robust underwater epoxy adhesives. The epoxy curing agent with an adaptive molecular architecture is first synthesized via solvent-free ring-opening polymerization of naturally occurring thioctic acid propelled by dynamic thiol-disulfide exchange. Upon combining the epoxy resin with poly(thioctic acid), the water-resistant long-chain polymers that effectively expel interfacial water and establish multiple interfacial interactions are formed by the first-stage curing via a click reaction between thiol and epoxy groups initiated by the thiol-disulfide exchange mechanism. Subsequently, the second-stage curing is triggered via carboxyl-epoxy reactions and leads to the formation of cross-linked networks. This strategy endows the developed underwater epoxy adhesive with underwater bonding strength up to 16.4 MPa and green recyclability that can be repeatedly disassembled.