ELECTROCHEMICAL INVESTIGATIONS ON THE SOL-GEL POLYMERIZATION OF TRANSITION-METAL ALKOXIDES

The kinetics of polymerization of zirconium propoxide has been studied under various conditions using an original electrochemical method. Th e alkoxides were complexed with bidentate ligands some of which were f unctionalized by ferrocene electroactive moieties. The bound electroac tive ferrocene component diffusion is used as a probe for determining the mass variation of the oligomers formed through the hydrolysis-cond ensation process. Chronoamperometry provided a means for studying diff usion kinetics. In this way polymerization kinetics can be followed wi th a fair precision on a real timescale, provided that the electroacti ve probe binds irreversibly to the polymerizing zirconium species. Two organic complexants, acetylacetone and ethyl acetoacetate, have been used in this study, in order to obtain gels from the highly reactive z irconium n-propoxide. The binding part of the electroactive probe was the strongly complexant salicylate ligand. The electrochemical results reveal the kinetics of polymerization, and give in addition an estima tion of the mobile species present once the system has reached a stabl e state. The results have been confirmed by several other techniques i ncluding SEM, elemental analysis, light diffusion and BET specific sur face determination on the resulting xerogels.