Dual dynamic crosslinking of rubber for enhanced mechanical properties and reconfigurable shape memory behavior

Constructing dynamic covalent bonds (DCBs) in rubbers provides a promising avenue to resolve the trade-offs between chemical crosslinking and recyclability. The reinforcement of dynamic covalent networks by nanofilling is widely adopted, which, however, inevitably hinders the exchange reaction of DCBs and network rearrangement due to the restrictions on chain mobility imposed by fillers. To date, the reinforcement of dynamic covalent networks without affecting the dynamic properties remains challenging. In this work, we report a dual dynamic crosslinking strategy by engineering reversible noncovalent bonds into dynamic covalent rubbers to improve mechanical performance and simultaneously maintain desirable malleability and reprocessability. Specifically, dynamic boronic ester-crosslinked styrene–butadiene rubber is firstly prepared and then modified through triazolinedione (TAD) click reaction. The grafted urazole groups can form hydrogen bond interactions that further aggregate to form clusters and phase-separation structure in the networks. Due to the reversible nature of hydrogen bonds, they can act in a sacrificial manner to dissipate mechanical energy, leading to a combination of improved strength, modulus and toughness of the networks. More importantly, the hydrogen-bonded clusters are dissociated at elevated temperatures, enabling the network dynamic properties to be largely preserved. In addition, the dynamic features of the dual crosslinks (hydrogen bonds and boronic esters) endow the TAD-modified networks with reconfigurable shape memory effect.