By incorporating copper sulfate （CuSO4） particles into acrylonitrile butadiene rubber （NBR） followed by heat pressing, a novel vulcanization method is developed in rubber through the formation of coordination crosslinking. This method totally differs from traditional covalent or non-covalent vulcanization approaches of rubber. No other vulcanizing agent or additional additive is involved in this process. By analyzing the results of DMA, XPS and FT-IR, it is found that the crosslinking of CuSO4 particles filled NBR was induced by in situ coordination between nitrogen atoms of nitrile groups （-CN） and copper ions （Cu^2＋） from CuSO4. SEM and EDX results revealed the generation of a core （CuSO4 solid particle）- shell （adherent NBR） structure, which leads to a result that the crosslinked rubber has excellent mechanical properties. Moreover, poly（vinyl chloride） （PVC） and liquid acrylonitrile-butadiene rubber （LNBR） were used as mobilizer to improve the coordination crosslinking of CuSO4/NBR. The addition of PVC or LNBR could lead to higher crosslink density and better mechanical properties of coordination vulcanization. In addition, crystal water in CuSO4 played a positive role to coordination crosslinking of rubber because it decreased the metal point of CuSO4 and promoted the metal ionization.
The most common way of rubbers for obtaining high performance is vulcanization, by which the linear macromolecules are crosslinked into three-dimensional networks. The rubbers vulcanized by covalent bonds are serious pollutants. There has been an increasing interest in the novel rubbers crosslinked by supramolecular interactions such as hydrogen bonds and ionic bonds because of the supramolecular interactions are reversible and the crosslinked materials are likely to be recycled. In this paper, a series of novel NBR/PVC materials crosslinked with CuSO4 by coordinate bonds were prepared for the first time, and the produced materials have excellent mechanical properties. In this system, the coordinate bonds formed in situ during the heat press process. XPS and SEM results prove that there are really crosslinks by coordinated bonds between the polymers and the CuSO4 particles. The characterizations of mechanical properties, crosslink densities and the temperature of glass transition all showed that degree of crosslink and the performance of the coordinated materials could be adjusted controllably.
