Facile strategy to incorporate amidoxime groups into elastomers toward self-crosslinking and self-reinforcement

Covalent crosslinking and reinforcement are two critical issues in elastomer science and engineering. It remains challenging to achieve green crosslinked and mechanically robust elastomer materials through a facile and efficient strategy. In the present work, a facile and novel strategy for multi-crosslinking network design is proposed to prepare high-performance elastomers based on the amidoxime modification of commercial nitrile-butadiene rubber (NBR). For the first time, we found that amidoxime-functionalized NBR (AO-NBR) shows unique self-crosslinking and self-reinforcing abilities. The hydrogen bonds and metal-ligand coordination bonds arising from amidoxime groups can be formed between the AO-NBR chains. Moreover, AO-NBR could be chemically self-crosslinked based on the reaction between amidoxime groups and nitrile groups without additional additives at elevated temperature, generating the 1,2,4-oxadiazole groups. Based on the inherent properties of AO-NBR, the multi-crosslinking network structures including covalent crosslinking bonds, physical hydrogen bonds, and metal-ligand coordination bonds could be constructed by a simple hot-pressing process and the introduction of zinc ions. What's more, the hydrogen bonds and Zn-based coordination bonds as sacrificial motifs can break prior to covalent bonds with large energy dissipation and undergo reversible breaking and reforming under an external force, which endows the AO-NBR with self-reinforcing ability. Hence, the obtained elastomers show excellent mechanical properties, and their tensile strength, modulus, and toughness are improved simultaneously. Overall, we envisage that this work may open up new avenues to design high-performance elastomers based on a facile self-crosslinking and self-reinforcing strategy.