Construction of dual coordination networks in epoxidized butadiene-acrylonitrile rubber/CuSO4 composites and mechanical behaviors

Dual coordinated cross link networks were designed in epoxidized butadiene-acrylonitrile rubber (NBR)/CuSO4 composites to make commercial NBR become advanced soft materials. First, NBR was modified through organic peroxy acid method to produce epoxidized butadiene-acrylonitrile rubber (ENBR). Next, CuSO4 was introduced in bulk to form strong Cu2+-nitrile coordination bonds acting as strong cross link points and Cu2+-epoxy bonds acting as weak cross link points. XPS analysis, FT-IR spectra and rheological curves proved the dual coordination bonds. Curing rheology curves, crosslinking density and thermal properties effectively demonstrated the formation of related dual cross link networks. The ENBR/CuSO4 composites exhibited excellent mechanical properties due to the synergistic effect of strong and weak metal-ligand coordination networks. During stretching, the weak coordination bonds acted as sacrificial bonds which could dissipate energy, while the strong coordination bonds sustained the network and imparted the elasticity. Under the combined functions of dual coordination bonds, the modulus, tensile strength, and toughness of ENBR/CuSO4 composites could be improved and tuned by controlling the structure parameter of coordination networks such as epoxidation degree and content of CuSO4.