Hybrid materials based on the reaction of polyorganophosphazenes and SiO 2 precursors
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Hybrid materials based on the reaction of polyorganophosphazenes and SiO2 precursors M. Guglielmi and G. Brusatin Dipartimento di Ingegneria Meccanica, Settore Materiali, Universit`a di Padova, Via Marzolo 9, 35131 Padova, Italy
G. Facchin Centro di Chimica Metallorganica del C.N.R., Istituto di Chimica Industriale, Facolt`a di Ingegneria, Universit`a di Padova, Via Marzolo 9, 35131 Padova, Italy
M. Gleria Istituto di Fotochimica e Radiazioni d‘Alta Energia del C.N.R., Sezione di Legnaro, Via Romea 4, 35020 Legnaro PD, Italy (Received 13 December 1994; accepted 29 January 1996)
New molecular composite materials can be prepared based on an inorganic oxide network and an organic polymer. The polymeric component generally requires low process temperatures, due to the presence of the organic backbone or side groups. A sol-gel process therefore is suitable for synthesizing the inorganic component by dissolving soluble polymers into sol-gel precursor solutions in order to obtain ceramic and polymeric solid phases. In this work polyorganophosphazenes were used because they have many technologically interesting properties (chemical, optical, electrical, mechanical). The methods to obtain covalent bonds between polymer and inorganic network and to obtain homogeneous, transparent hybrid materials without phase separation were studied. It was possible to avoid phase separation by preparing phosphazenes containing free hydroxyl functions and by adequately choosing the experimental conditions.
I. INTRODUCTION
Recently, molecular composite materials, based on inorganic oxide networks and organic polymers, have been prepared and described in the literature.1,2 Since the synthesis of the materials requires low process temperatures due to the presence of the polymeric component, the sol-gel process is largely used in such preparations. The procedure followed generally involves the dissolution of soluble polymers into a sol-gel precursor solution and the formation of materials in which ceramic and polymeric solid phases are intimately mixed. In addition, by an appropriate choice of the polymers and inorganic precursors, not only interpenetrating networks, but materials, in which real chemical bonds are formed between the polymer and the inorganic component, can be obtained.1 As a result, these molecular composite materials are often highly transparent, giving an enormous number of new applications with properties different from those of the individual materials. Generally speaking, the organic component can enhance the toughness of brittle inorganic materials, and the inorganic network can increase the scratch resistance and hardness of plastics. Furthermore, functional organic groups can be introduced into the rigid and mechanicalJ. Mater. Res., Vol. 11, No. 8, Aug 1996
resistant inorganic matrices to obtain specific (chemical, optical, electrical, etc.) properties. Polyphosphazenes are polymers characterized by many interesting technological properties,3–6 such as flame-retardancy
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