Good linear relationship between logarithms of Eigen’s water exchange constants for several divalent metal ions and activation energies of corresponding metal-catalyzed alkoxysilane hydrolysis in ethylene–propylene copolymer system

Catalytic efficiencies of seven divalent metal acetylacetonate complexes [M(acac)2; M = Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II)] with respect to the water-crosslinking kinetics of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-VTMS) were investigated to examine the effects of progressive changes in metal ion using ATR–FTIR spectroscopy. The hydrolysis activation energies of EPR-g-VTMS follows the order: No catalyst ≈ Ni(acac)2 > Co(acac)2 > Fe(acac)2 ≈ Zn(acac)2 > Cd(acac)2 ≈ Cu(acac)2 > Pb(acac)2. Interestingly, the kinetics results revealed that the plots of hydrolysis activation energies of EPR-g-VTMS containing M(acac)2 complexes and Eigen’s water exchange constants for corresponding metal ions showed a excellent linear relationship, suggesting that the reaction pathway for the silane water-crosslinking with hydrous M(acac)2 complex in EPR-g-VTMS system may be similar to that for water exchange of the metal ion in an aqueous system. Based on the knowledge of traditional kinetics studies by Eigen and Wilkins and hybrid sol–gel chemistry, the plausible catalytic mechanism for M(acac)2 complexes in EPR-g-VTMS system was proposed.