Novel organo-functional titanium-oxo-cluster-based hybrid materials with enhanced thermomechanical and thermal 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.