Exploring Copper-Amino Acid Complexes in Cross-Linking of Maleated Ethylene Propylene Rubber

Herein, we report a network of maleic anhydride-grafted ethylene propylene rubber (M-EPM) cross-linked by the coordination complexes that combines high tensile strength, high stretchability, and reprocessability aspects. At appropriate temperatures, coordination cross-linked M-EPM rubber can be easily reprocessed without compromising physical properties. At first, we demonstrate the synthesis and characterization of coordination complexes of two types of amino acids, that is, L-lysine and L-tryptophan, which form a complex with Cu(II) ion through their respective amino acid group. As followed by various analyses, these complexes of L-lysine and L-tryptophan exhibit a distinct behavior after incorporation into M-EPM rubber. The copper-ligand bonds can easily break and reform, while the copper center remains attached to the amino acid ligands through a stronger interaction with the carboxylic group, which enables the highly dynamic stress-induced ion exchange process. This notion is firmly endorsed by the enhanced physicomechanical attributes of M-EPM rubber and the recyclability aspect.