Zirconium alkoxides as components of hybrid inorganic-organic macromolecular materials

Two types of inorganic-organic hybrid materials were prepared in a one-step process by mixing zirconium butoxide or propoxide and 2-hydroxyethyl methacrylate (HEMA) with or without benzoyl peroxide (BPO). The reaction of the alkoxides with HEMA was followed by IR, NMR, and DSC analyses, performed at different times after the mixing. NMR experiments suggest that free HEMA monomer is in fast exchange with that linked to zirconium ions. The mixtures containing BPO polymerized and stiffened in a few minutes after a mild thermal treatment. The hybrid materials are homogeneous and transparent, but brittle as well. Cerium(III) 2,4-pentanedionate was also added to modify the reactivity of zirconium alkoxides, and its role is invoked to account for the occurring free radical polymerization at room temperature. The formation of these HEMA-zirconia hybrid materials, showing glassy behavior and a remarkable thermal stability, is accompanied by low shrinkage.