Cluster-Crosslinked Inorganic-Organic Hybrid Polymers: Influence of the Cluster Type on the Materials Properties
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Cluster-Crosslinked Inorganic-Organic Hybrid Polymers: Influence of the Cluster Type on the Materials Properties Silvia Gross, Vito Di Noto,1 Guido Kickelbick and Ulrich Schubert* Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9/165, A-1060 Wien, Austria 1 Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universita degli Studi di Padova, via Loredan, I- 35100 Padova, Italy
ABSTRACT Methacrylate-substituted tetranuclear tantalum, zirconium and titanium oxide clusters (Zr4O2(OMc)12, Ti4O2(OPri)6(OMc)6, and Ta4O4(OEt)8(OMc)4) were prepared by reaction of the alkoxides with methacrylic acid. The clusters were then polymerized with methyl methacrylate as co-monomers in different molar ratios (0.5–2 mol% of the functionalized cluster). In the resulting inorganic-organic hybrid polymers, the clusters crosslink the polymer chains very efficiently. The physical properties and structural features of the hybrid polymers, investigated by their swelling behavior, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), 13C MAS NMR and impedance spectroscopy, exhibit a clear dependence on the cluster portion in the polymer and on the cluster type. INTRODUCTION The basic idea behind the development of inorganic-organic hybrid materials is the combination of inorganic and organic moieties on a molecular scale to achieve a synergetic combination of the properties typical of each of the constituents. The materials properties are not only determined by the kind and portion of the organic and inorganic moieties, but also by their structure and mutual arrangement, and by the interface between both. Modification of these parameters allows, in principle, a deliberate tailoring of the materials properties. One of the most versatile methods for the preparation of inorganic-organic hybrid materials is sol-gel processing, which allows the formation of the inorganic entities starting from molecular precursors. There are three approaches to prepare such hybrid materials in which the inorganic and organic entities are connected by strong covalent bonds: 1. Formation from compounds of the type [(RO)nM]xY, in which Y is an organic group or polymer chain linking two (x = 2) or more (x > 2) metal alkoxide units, M(OR)n [1]. The inorganic structures are formed by sol-gel processing of the M(OR)n groups. 2. Pre-formation of functionalized inorganic building blocks from metal alkoxides followed by polymerization of organic functions attached to the inorganic core [2]. 3. Formation from bifunctional molecular precursors (RO)nM–X–A bearing a hydrolyzable inorganic group (RO)nM, and an organic functionality (A) capable of undergoing polymerization or crosslinking reactions [3]. The hybrid polymers are formed by a combination of sol-gel processing and organic polymerization reactions. For the development of inorganic-organic hybrid materials, the third approach is most often used. Polymers in which pre-formed clusters as nanosized inorganic building blocks are incorporated into organic po
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