Rubbery Ormosils
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RUBBERY ORMOSILS
Young J. Chung, Su-Jen Ting and John D. Mackenzie Department of Materials Science and Engineering, University of California, Los Angeles, CA 90024 ABSTRACT A new technique which permits the successful preparation of ORMOSILS (Organically Modified Silicates) with rubbery elasticity has been developed. Common alkoxides were reacted with polydimethyl siloxane (PDMS) and the microstructures were carefully controlled. Large monoliths of the porous 29 Si rubbery ORMOSILS have been prepared. Gelation process was studied by liquid NMR spectroscopy. A structural model for rubber elasticity of ORMOSILS was proposed. INTRODUCTION Inorganic materials, such as glasses and ceramics, although they have high temperature stability, are brittle and not easily fabricated into large or complex shapes. Recently, oxide glasses and ceramics have been fabricated at relatively low temperatures by a new technology known as the "sol-gel" process [1,2]. Although the fabrication temperatures have been significantly lowered, the resulting materials, because they have all oxide bonds, are still brittle. Also, these materials tend to fracture during drying and heattreatment.because of the porosity of gels. More recently, pure oxide gels have been modified by the incorporation of organic groups to improve the ductility . Some of these materials are known as ORMOSILS (Organically Modified Silicates)[3], and "Ceramers"[4]. ORMOSILS are less brittle and show less tendency to fracture, because some of the bonds are terminated by organic side groups. Although ORMOSILS are less brittle than pure oxides, rubbery behavior of ORMOSILS has not been reported. In this paper, a new technique which permits the successful preparation of rubbery ORMOSILS will be discussed. EXPERIMENTAL Tetraethoxysilane (TEOS) was used as inorganic component and polydimethyl siloxane (PDMS) was used as the polymeric component. The appropriate amount of TEOS (Alfa Products) and silanol terminated PDMS oligomer with MW= 1700 (Petrach System) were mixed with organic solvents, distilled water and acid catalyst. The solutions were reacted at elevated temperatures (70 C - 100 C) and cooled to room temperature. The solutions were cast into molds and sealed. After gelation, the wet gels were dried. Gelation time was measured by the tilt method. Sample densities were measured by the Archimedes method. 29Si liquid NMR spectroscopy was performed to study the reaction process. Solution samples were transferred, during the reaction, into the NMR sample tube and quenched immediately in liquid nitrogen. Frozen samples were melted just before the NMR spectroscopy was performed. 2 9 Si NMR spectra were recored on a AM360 BRUKER spectrometer. A pluse width of lOps was applied with a relaxation delay of 6s. TMS was used as a reference. The microstructure of the gel was studied by scanning electron microscopy (SEM). The mechanical Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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properties were measured using an Istron Model 1122. RESULTS AND DISCUSSION
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