Toughening, recyclable and healable nitrile rubber based on multi-coordination crosslink networks after “tetrazine click” reaction

[Display omitted] •The “tetrazine click” reaction of nitrile rubber.•Multiply metal-ligand coordination crosslink networks.•Reinforced mechanical strength and toughness.•Excellent recycling and heat-healing ability. The recycling and self-healing functions of commercial rubber are of great significance in the field of sustainable materials. So far, manufacturing such rubber with excellent strength and toughness was still a huge challenge. Herein, the multi-coordination crosslink networks were designed to achieve this goal. First, the nitrile-butadiene rubber (NBR) was modified through 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPT) click reaction to introduce the second ligand group. Next, the blend of modified NBR and metal salt (including ZnCl2 and CoCl2) was hot-pressed to form the metal-nitrile and metal-pyridine (nitrogen-containing heterocyclic groups) coordination bonds. The designed composite had ultra-high mechanical strength and toughness at the same time. Compared with the NBR/ZnCl2 composite, the tensile strength of NBR-DPT4-Zn10 composite with multi- coordination bonds was improved by 7.5-fold (from 5.5 MPa to 46.82 MPa), and the corresponding fracture energy was improved by 142% (from 26.2 MJ m−3 to 63.5 MJ m−3). At the same time, the high recyclable and heat-healing efficiency were obtained. These achievements are expected to develop commercial rubber’s recyclability and high mechanical properties.