The Synthesis, Structure and Property Behavior of Inorganic-Organic Hybrid Network Materials Prepared by The Sol Gel Pro
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THE SYNTHESIS, STRUCTURE AND PROPERTY BEHAVIOR OF INORGANIC-ORGANIC HYBRID NETWORK MATERIALS PREPARED BY THE SOL GEL PROCESS G.L. WILKES, A.B. BRENNAN, HAO-HSIN HUANG, DAVID RODRIGUES AND BING WANG Dept. of Chemical Engineering, Polymer Materials & Interfaces Laboratory, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061 ABSTRACT The synthesis, structure/property behavior of inorganic-organic hybrid network materials prepared by the sol gel process have been chronologically reviewed with emphasis on those systems prepared in the authors laboratory. Specific features of reactions as well as the nature of reactants are included. The morphological features of these "ceramer" systems formed have many features in common even though the reactants may be quite different. The mechanical properties of the final materials in conjunction with SAXS have proven beneficial in establishing the basics of their morphological texture. Finally, it is demonstrated how microwave radiation in some cases, can serve as an efficient way in processing the ceramer systems. INTRODUCTION In 1985 work was initiated within our laboratories with the objective being to develop novel organic-inorganic hybrid network materials by reacting metal alkoxides with functionalized polymeric/oligomeric species by the sol gel process [1]. This paper addresses this topic with emphasis on work from our laboratory but also will touch upon related work of others. Since the authors will principally address their research, omissions to the other workers has not been by design but is due to space limitations. The classic sol gel reaction generally involves both the hydrolysis and condensation of metal alkoxides. Generally, these two reactions occur simultaneously once the hydrolysis step has been initiated. The reaction rates of each are highly dependent upon such variables as the temperature, pressure, local pH, nature of the metal alkoxide and the environment in which the reaction takes place (e.g. concentration of water, alcohols and other solvent media components utilized). Of course, the condensation step generally lead to loss of a water molecule while each hydrolysis step leads to the production of an alcohol component - both of these features contribute to the high shrinkage that occurs during the sol-gel process. However, there is still much more information needed to understand the classical sol gel reactions. Our goal, however, has not been to focus on these features as much as to utilize the sol gel reactions of metal alkoxides as a means of developing new materials by the incorporation of appropriately functionalized organic oligomeric/polymeric components. Restated, the goal has been to incorporate both inorganic and organic based materials into a single network system that may possess properties that are either unique and/or somewhat intermediate between those of the pure organic and pure inorganic networks. They might also allow control of a wide range of refractive index values and at the same time the material may still retain
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