Features of Microwave Processing of Inorganic/Organic Hybrid Networks (Ceramic) Materials.
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FEATURES OF MICROWAVE PROCESSING OF INORGANICIORGANIC HYBRID NETWORKS (CERAMIC) MATERIALS.
D. E. RODRIGUES and G. L. WILKES Polymer Materials and Interface Laboratories Department of Chemical Engineering Virginia Polytechnic Institute & State University Blacksburg, Va 24061. INTRODUCTION
Over the last two decades the sol gel technique has become very popular because of its ability to yield a multicomponent inorganic glass at low temperatures[I,2]. More recently, techniques to incorporate organic species into a sol gel network of metal alkoxides has been developed and studied[3-7]. One technique developed in our laboratory is to incorporate oligomers endcapped with metal alkoxide functionalities into a reaction mixture of TEOS, water and acid catalyst. The resulting materials, often cured at ambient temperatures, can be tough and transparent monoliths. This technique is important in that it helps to overcome some of the defects of pure sol gel silicate structures such as cracks, voids and brittleness. The high temperature structural properties of these materials, however, are limited because of the organic component. This approach provides the ability to make a wide range of materials with vastly different properties depending upon the polymer and metal alkoxide chosen. Novel properties displayed by these materials make them attractive for certain technological applications such as coatings, films and fibers. One of the main drawbacks of the ambient temperature curing process is the relatively long reaction time which hinders immediate utilisation of the product. As would be expected, the extent of reaction has been found to be dependent on the T, of the oligomer under consideration. In the case of high Tg oligomers (e. g. polysulfones) the reaction has to be completed at elevated temperatures (above the T.) in order to acheive a high extent of reaction. In the case of ceramers containing functionalized poly(tetramethyleneoxide) (PTMO) oligomer, curing time can vary between 48 to 100 hours before the final gel can be successfully handled and tested. In order to enhance the rates of reaction and determine the effect of such an acceleration on the physical properties, samples were reacted at elevated temperatures using microwave heating and conventional oven curing. When microwaves were used the curing time has been found in some cases to be reduced dramatically from 60 hours to twenty minutes. In this paper structure-property relationships of these "microwaved" materials will be compared and contrasted with similar materials cured in a conventional oven at equivalent elevated temperatures as well as room temperature cured materials. Time-temperature studies of the reactants were also conducted in a travelling wave guide. These studies were done primarily to gain some insight as to the effect of microwaves on specific reactants. analyzer. EXPERIMENTAL
Sample formulation for the experiment consisted of 60wt% of TEOS with the remainder constituted by triethoxysilane endcapped PTMO of a number average molecular weight
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