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Titanium-oxo clusters are employed as inorganic nanobuilding blocks in order to obtain new organic-inorganic hybrid materials. Nanobuilding blocks are well-defined preformed entities which allow a better control of the inorganic domains for the elaboration of hybrid nanocomposites. The oxo-alcoxo cluster Ti16O16(OEt)32 presents a shell of labile ethoxy groups which can be selectively exchanged with preservation of the oxo-core. Both the kinetics of the solvolysis and the number of substituted titanium atoms are strongly dependent on the nature of the reactants. The post-modification of the cluster lead to the elaboration of new oxo-alcoxo clusters Ti16O16(OEt)32- x(OR)x (R : alkyl, phenyl… groups) and when polymerizable ligands, such as methacrylate or styrenic ligands, are introduced at the surface of the nanobrick, new functional nanobuilding blocks can be obtained. These functional clusters are then copolymerized with organic monomers leading to 3D networks where the inorganic nano-fillers are covalently linked to the organic polymer and act as very effective nano-cross-linker. These nanobricks can be considered as good models to correlate the structure of hybrid materials and their physical properties especially their mechanical, thermal, and optical properties.

Titanium-oxo clusters are employed as inorganic nanobuilding blocks in order to obtain new organic-inorganic hybrid materials. Nanobuilding blocks are well-defined preformed entities which allow a better control of the inorganic domains for the elaboration of hybrid nanocomposites. The oxo-alcoxo cluster Ti16O16(OEt)32 presents a shell of labile ethoxy groups which can be selectively exchanged with preservation of the oxo-core. Both the kinetics of the solvolysis and the number of substituted titanium atoms are strongly dependent on the nature of the reactants. The post-modification of the cluster lead to the elaboration of new oxo-alcoxo clusters Ti16O16(OEt)32- x(OR)x (R : alkyl, phenyl… groups) and when polymerizable ligands, such as methacrylate or styrenic ligands, are introduced at the surface of the nanobrick, new functional nanobuilding blocks can be obtained. These functional clusters are then copolymerized with organic monomers leading to 3D networks where the inorganic nano-fillers are covalently linked to the organic polymer and act as very effective nano-cross-linker. These nanobricks can be considered as good models to correlate the structure of hybrid materials and their physical properties especially their mechanical, thermal, and optical properties.

Two novel nanomaterials based on hybrid organic−inorganic polymers have been prepared via free radical polymerization of (I) dimethacrylate oligomers and (II) 2-hydroxyethyl methacrylate (HEMA) in the presence of different contents of organically modified titanium−oxo-clusters Ti16O16(OEt)24(OC2H4Mc)8 (OMc = methacrylate). Investigations, combining small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and energy-filtering transmission electron microscopy (EFTEM) lead to consistent structural and morphological characteristics for both grades of hybrid materials. Structural features, such as the subunit size and fractal dimensions are extracted from SAXS profiles. For the first grade of nanomaterials, i.e., for different content of titanium−oxo-clusters (2.5, 5 and 7.5 wt %) incorporated into a dimethacrylate-based matrix, aggregates with ramified mass fractal structures were found. Semiquantitative studies of TEM and EFTEM images revealed the presence of a uniform size distribution in the case of 2.5 wt % titanium cluster content with a typical size of 30 nm. A larger size distribution has been found for the 5 wt % and 7.5 wt % between 30 and 180 nm. For the second grade of nanomaterials, i.e., the 19.2 wt % of organically modified titanium clusters incorporated into poly(HEMA), compact and highly dense aggregates with a size distribution from a few nm up to 50 nm were found from TEM and EFTEM images. A significant increase of the storage modulus for the first grade of nanomaterials was revealed by dynamic mechanical analysis (DMA). The incorporation of Ti nanoclusters in the matrix lead to a significant alteration of the system's hardness as indicated through nano-indentation measurements. Thermogravimetric analysis also indicated a significant enhancement of the thermal stability compared to the neat matrix, probably because of the antioxidant effect of the titanium−oxo-clusters.

Transparent monoliths made of new interpenetrating networks based on titanium-oxo-polyhydroxyethyl methacrylate PHEMA nanocomposites are obtained through one pot synthesis with low shrinking and show a strong laser-induced darkening activity.

The elaboration of porous materials by using metal alkoxides (Ce(O-iPr)4, Ti(OR)4) as inorganic precursors and acid functionalised dendrimers as organic templates is reported. Chelation by COOH groups present at the dendrimer surface was used to control the reactivity of the metal oxide precursors, creating at the same time anchoring points for the nucleation of a gel phase. The bicontinuous gels resulting after solvent evaporation present a “sponge-like” structure with pore size ranging from 10 to 30 nm. The effect of the metal/dendrimer ratio, the sol preparation procedure and aging conditions were studied by XRD, FTIR, TEM, SEM and BET.

AbstractAmong other soft chemistry processes, sol-gel chemistry offers a versatile access to chemically designed new hybrid organic-inorganic materials. Two approaches to synthesize hybrids are presented: the hydrolysis of organo functional metal alkoxides or the assembly of nanobuilding blocks.