A designer Schiff based motif offered dual dynamic exchangeable bonds, faster curing and closed‐loop circularity in epoxy vitrimers

Abstract

AbstractA fast‐curing epoxy with improved mechanical properties, self‐healing and re‐processability was designed using a tailored Schiff based motif that offered dual covalent adaptable network (CAN) in epoxy. The designer motif is a dynamic hardener with both acetal linkage and a Schiff base motif in the same molecule which allowed us to gain a mechanistic insight into the evolving transient network in epoxy vitrimers. The dynamic hardener besides offering a cross‐linked network in epoxy can facilitate rapid exchange reactions, resulting in a material with high tensile strength (74 MPa), high glass transition temperature (121°C), and that can be re‐purposed through solvent induced degradation. The proposed dynamic curing agent is suitable to be employed as a coating material on substrates to ensure excellent self‐healing and re‐processability ensuring chemical recyclability. Few carbon fiber‐based laminates were prepared using the epoxy vitrimer and the recovery of CF post laminate preparation clearly demonstrates the closed‐loop circularity in epoxy vitrimers.Highlights A unique dynamic curing agent is designed consisting of an aldehyde (salicylaldehyde) and an amine and acetal containing species (amino acetaldehyde dimethyl acetal). It facilitates imine and acetal exchange that can bond at temperatures <60°C and break at temperatures >105°C as evidenced by the vitrimer transition temperature. Epoxies show high tensile strength (74 MPa), exceptional Tg (121°C), fast stress relaxation and an activation energy of 96.2 KJ/mol. The imine‐acetal exchange system rendered the epoxies re‐processable, malleable and re‐usable.