Preparation of Particulate Core-Shell Metal Oxide-Polymer Nanocomposites by a Sol-Gel Approach
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Preparation of Particulate Core-Shell Metal Oxide-Polymer Nanocomposites by a Sol-Gel Approach
Guido Kickelbick, Dieter Holzinger Vienna University of Technology, Institute of Materials Chemistry, Getreidemarkt 9, A1060 Wien, Austria, E-mail: [email protected] ABSTRACT Two general microemulsion-based routes towards surface-functionalized metal oxide nanoparticles serving as macroinitiators in “grafting from” atom transfer radical polymerization (ATRP), are presented. Metal alkoxides modified with several β -diketone derivatives carrying potential ATRP-initiating sites served as precursors for the particle formation leading in an solgel process to in situ-functionalized titanium-, zirconium-, tantalum-, vanadium-, yttrium-, and iron oxide nanoparticles. The obtained systems were compared with metal oxide nanoparticles prepared by using metal salts as precursors which were functionalized in a second step with ATRP-initiator containing silane coupling agents. The obtained particles had diameters between 5 nm and 640 nm and served as multifunctional polymerization initiators in ATRP using styrene and methyl methacrylate as monomers.
INTRODUCTION Inorganic nanoparticles with various chemical composition recently attracted much interest because of their properties arising from their dimension between that of molecules and bulk materials and their large surface areas.[1] Both properties are important for many potential applications of nanometer-scaled systems in electronics,[2] optics,[3] catalysis,[4] and many others. However, a lot of potential device applications require the incorporation of the nanoparticles into a matrix that is often incompatible with the inorganic moiety, due to less favourable interactions between the particle surface and the matrix. The resulting inorganicpolymer nanocomposites are highly interesting materials because of the unique combination of properties in one material. For example thermal or mechanical properties of a polymer can be extremely enhanced if inorganic moieties are incorporated.[5] Many of the unique nanocomposite properties are based on the homogeneous and stable distribution of the nanoparticles in the polymer matrix. However, in many cases if inorganic nanoparticles are incorporated into an organic monomer or polymer agglomeration occurs due to their high surface energy and the incompatibility of the two components. This can lead to neutralization of the individual nanoparticle properties but also to inhomogenization and micro phase separation in the material. Surface-functionalization of the colloidal systems with organic groups that act as a compatibilizer between the inorganic particle core and the organic matrix is carried out to overcome these problems. Many capping agents, such as surfactants[6] or polymers[7] were already applied which prevent agglomeration and further growth of the nanoparticles or lead to stable dispersions of the particles in organic solvents. Surface-functionalization can also lead to novel chemical properties of the particles
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