Leveraging orthogonal dynamic chemistries to engineer tough and reprocessable double networks

Double networks, comprised of a pre-stretched stiff filler network embedded within a soft matrix network, are a promising class of elastomers that are tough and elastic. A critical feature of these materials is their ability to dissipate significant energy from the sacrificial scission of filler bonds ahead of the crack tip. Their increased fracture toughness enables longer service lifetimes but once they undergo failure, like conventional elastomers, they cannot be recycled and end up in landfills. This lack of processability stems from the static nature of covalent bonds in both filler and matrix networks. One way of overcoming this limitation is to introduce dynamic covalent bonds into the system. Here, we leverage orthogonal dynamic chemistries and design a double network with an associative boronate ester filler network and a dissociative thia-Michael matrix network. By tuning the composition of the double networks and characterizing their mechanical properties at both small and large strains using rheology and tensile testing, we demonstrate that with the right thermal treatment, these double networks can be mechanically robust and fully reprocessable.