Enhancing catalytic activity of copper(II) complexes by curcuminoid as electron-withdrawing ligand for silane water-crosslinking reaction: a joint experimental and theoretical study

The catalytic performances of several copper(II) beta-diketonate (Cu(II)(beta DiK)(2)) complexes for the water-crosslinking reaction in the 3-methacryloxypropyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-MTMS) system were investigated. UV-vis spectroscopic measurements demonstrated the curcuminoids could strongly coordinate with copper(II) ion. Moreover, results of the kinetic examination revealed the good linear relationship between the stability constants and hydrolysis activation energies in the Cu(II)(beta DiK)(2) catalyzed EPR-g-MTMS system, suggesting the stability of Cu(II)(beta DiK)(2) complex was a very good catalytic activity predictor. The theoretical calculations demonstrated that the electron-withdrawing curcuminoids pulled the electron density from Cu2+ center to form the stable complex and decreased water-dissociation energy of axially coordinated water molecules with copper(II) ion. The results clearly show the beta-diketone ligands affect the water-exchange reaction of copper(II) ion, resulting in the enhanced catalytic activities of Cu(II)(beta DiK)(2) complexes for the silane water-crosslinking reaction. Our results provide a promising potential to use metal-curcuminoids in the room-temperature-vulcanizing silicone rubber applications. A good linear relationship between stability constants of the copper(II) beta-diketonate (Cu(II)(beta DiK)(2)) complexes and hydrolysis activation energy in the Cu(II)(beta DiK)(2) catalyzed silane-grafted polyolefin systems was observed. Our results also provide a promising potential to use metal-curcuminoids in the room-temperature-vulcanizing silicone rubber applications. [GRAPHICS] .