Precursors metal-organic polymers

Another potential source of processlble precursors Is the citric acid/ethylene glycol system which has been esiployed previously in the preparation of highly dispersed perovskite, spinel and related complex oxides. This method provides soluble, metal-organic, polymer precursors which have been used for the fabrication of oxide thin films as well as for the production of oxide powders with excellent homogeneity, good stoichiometry control and uniform sizes at relatively low temperatures(13,14). 

Coordintion compounds and metal-organic polymers precursors of materials... 

Metal organic polymers were used with success in the synthesis of nanometals as well. In one of the reported applications of MOCPs as precursors, calcination in a closed furnace of [Cu3(BTC)J H BTC = 1,3,5-benzenetricarboxylic acid) that include besides compounds decomposition the reduction of the metallic cations determines the formation of coralloid microstructures with surface interspersed comprised of Cu nanoparticle clusters [160]. 

The spiro polymerization is a novel reaction type that uses the spiro dimerization of o-QMs to build up linear oligomers and polymers. The basic properties of the spiro dimer of a-tocopherol, that is, its fluxional structure and its ready reduction to the ethano-dimer, remain also active when such structural units are bound in the polymer. The products of the reaction, both in its poly(spiro dimeric) form (41) and in the form of the reduced polytocopherols (42), are interesting materials for application as high-capacity antioxidants, polyradical precursors, or organic metals, to name but a few. 

One potential solution to these problems, suggested some 20 years ago by Chantrell and Popper (1), involves the use of inorganic or organo-metallic polymers as precursors to the desired ceramic material. The concept (2) centers on the use of a tractable (soluble, meltable or malleable) inorganic precursor polymer that can be shaped at low temperature (as one shapes organic polymers) into a coating, a fiber or as a matrix (binder) for a ceramic powder. Once the final shape is obtained, the precursor polymer can be pyrolytically transformed into the desired ceramic material. With careful control of the pyrolysis conditions, the final piece will have the appropriate physical and/or electronic properties. 

Composite materials can be formed by numerous methods. Two modes in which incorporation of the inorganic material in the template can be achieved will be discussed sol-gel processes or nanoparticle infiltration. They are both solution methods that can be processed at low temperatures, hence allowing the use of polymeric templates. In the first method the sol-gel chemistry is performed after the incorporation of a metal oxide precursor in the polymer matrix or around the template entities. The second method makes use of preformed metal oxide nanoparticles, which are infiltrated into the organic scaffold or suspended in solution with the individual structures for controlled adhesion. 

Hybrid metal oxide/polymer monoliths are formed when sol-gel reactions are performed within the pore system of the organic gel [7, 8]. The alcohol soaked polymer gel is simply placed in the liquid precursor and then into an al-cohol/H20 solution for hydrolysis and condensation, which gives an amorphous metal oxide layer on the polymer surface. Heating the hybrid at 450 °C results in removal of the organic template and crystallization of the inorganic material. 

Martin and coworkers have demonstrated the use of cylindrical-pored templates for the preparation of tubes and fibers composed of metal oxides, metals and polymers [35,36]. Track-etching of polycarbonate films gives membranes with cylindrical pores that are randomly distributed across the membrane. The pore diameters are monodisperse and, in the example described here, are 600 nm. Lak-shmi et al. have used these membranes for the preparation of vanadium oxide fibers [36]. The pores of the organic filter were filled with vanadium(V) triiso-propoxy oxide in an argon atmosphere. Exposure to air at 60°C induces hydrolysis of the precursor before an oxygen plasma is used to remove the polycarbonate. The crystalline alpha phase vanadium oxide (V2O5) fibers obtained by this... 

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