The synergetic combination of inorganic and organic components at the molecular level is a challenging task in materials science and chemistry, offering a wide variety of possible applications. An important sub-class of inorganic-organic hybrid materials is represented by polymers reinforced with nanosized metal oxides with polymerizable surface ligands.
In the first part of the work hybrid materials were designed through the covalent connection of metal alkoxides to a polymer backbone and subsequent hydrolysis and condensation. In a first step compounds were prepared containing both a polymerizable bond and the precursor for the sol-gel process. The alkoxides could form the respective oxide materials through the sol-gel process, while the organic double bonds were used for the formation of a polymeric matrix by controlled radical polymerization techniques. Analyses of the hybrid materials revealed that they were composed of well-ordered metal oxide nanoparticles incorporated inside the polymer matrices. When methacrylate-type polymers were used as the organic matrix, the final materials showed enhanced mechanical and thermal properties. On the other hand, elastomers in form of polysiloxanes were also used as polymer matrices.
Their functionalization with similar metal alkoxide building blocks could be achieved through hydrosilation reactions. Either bulk materials of polysiloxane matrices with ordered metal oxide domains inside, or hybrid core-shell nanoparticle morphologies were obtained depending on the interactions of the backbone polymers with the solvents employed. The second part of the work was devoted to the synthesis of TiO2 anatase nanoparticles and their applications in photocatalysis. In this project we investigated the synthesis of photocatalytically active anatase nanoparticles with anisotropically surface-functionalization that protected one side of the particle, and their incorporation in polymeric matrices. The sol-gel process allowed the controlled design of particle size and morphology. After the optimization of the process monodispersed particles with diameters between 5 and 40 nm were obtained. These particles were anisotropically surface-functionalized with various ligands such as phosphonates and phosphates containing polymerizable groups using oil-in-water Pickering emulsions. Such 'Janus'-type particles showed a good activity in photocatalysis and can bond to organic surfaces through their organophosphorus coupling agents.
In the Pickering emulsion also hybrid architectures could be designed through polymerization inside of such emulsion droplets. The resulting materials were hybrid polymeric spheres of about 2 m whose surface was fully covered by the photocatalytically active TiO2 nanoparticles. In another approach the pristine titania nanoparticles were fully surface modified in solution, using the same type of organophosphorus coupling agents, and further on incorporated in polymeric matrices. The hybrid materials were optical transparent, and showed an increased thermal and mechanical stability.