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

• Published in: Journal of sol-gel science and technology Vol. 102; no. 2; pp. 322 - 334
• Main Authors: Tanaka, Shohei, Imamura, Mina, Adachi, Kenta
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.05.2022; Springer Nature B.V
• Subjects: Activation energy; Catalytic activity; Ceramics; Chelation; Chemistry; Chemistry and Materials Science; Composites; Coordination compounds; Copolymers; Copper; Crosslinking; Diketones; Electron density; Energy of dissociation; Free energy; Glass; Graft copolymers; Heat of formation; Hydrolysis; Inorganic Chemistry; Ligands; Materials Science; Nanotechnology; Natural Materials; Optical and Electronic Materials; Original Paper: Industrial and technological applications of sol–gel and hybrid materials; Polymers; Polyolefins; Propylene; Room temperature; Science; Silanes; Silicone rubber; Stability; Stability constants; Vulcanization; Water chemistry; Copper(II) β-diketonate complex; Alkoxysilane; Polyolefin; Water-crosslinking reaction; Catalyst; Curcuminoid
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-022-05773-5

The catalytic performances of several copper(II) β-diketonate (Cu(II)(βDiK) 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)(βDiK) 2 catalyzed EPR- g -MTMS system, suggesting the stability of Cu(II)(βDiK) 2 complex was a very good catalytic activity predictor. The theoretical calculations demonstrated that the electron-withdrawing curcuminoids pulled the electron density from Cu 2+ 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 β-diketone ligands affect the water-exchange reaction of copper(II) ion, resulting in the enhanced catalytic activities of Cu(II)(βDiK) 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) β-diketonate (Cu(II)(βDiK) 2 ) complexes and hydrolysis activation energy in the Cu(II)(βDiK) 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. Highlights The catalytic performances of Cu(II)(βDiK) 2 complexes for the water-crosslinking reaction in silane-grafted polyolefin system were investigated. Cu(II)(βDiK) 2 complexes showed a high catalytic activity for the hydrolysis reaction. Curcuminoid with electron-withdrawing substituents showed the good chelating ability with copper(II) ion to form the stable Cu(II)(βDiK) 2 complexes. Kinetic examination revealed the good linear relationship between the stability constants of the Cu(II)(βDiK) 2 complexes and hydrolysis activation energies in the Cu(II)(βDiK) 2 catalyzed EPR- g -MTMS system, suggesting the stability of Cu(II)(βDiK) 2 complex was a very good catalytic activity predictor.