Abstract
Epoxy-bridged alkoxysilane reactive precursor has been synthesized in this study by reacting DGEBA epoxy with 3-aminopropyltriethoxysilane. Nano hybrid composites structures were prepared and investigated from the combination of epoxy-bridged alkoxysilane reactive precursor with tetraalkoxysilcate and tetraalkoxy titanate through direct thermal curing process. The effect of catalyst on the structure and properties of the nanohybrid composites were also discussed and compared. FT-IR and 1H NMR were used to characterize the reactivity and structure of epoxy-bridged alkoxysilane reactive precursors. The cured hybrid composite structures of epoxy-bridged alkoxysilane with tetraalkoxysilane were investigated by 29Si CP/MAS NMR. TGA, TMA, and DMA were utilized to analyze the thermal and thermal mechanical properties of the cured epoxy bridged-polysilsesquioxane nanosilica composites. The optical properties of the cured epoxy bridged-polysilsesquioxane nano titanianoxide composites were also discussed in this study. The refactive index of the cured epoxy bridged-polysilsesquioxane nano titanianoxide composites were found to increase from 1.55 to 1.59 when 50 phrs of tetrabutyltitinate (TBT) was mixed with epoxy-bridged alkoxysilane reactive precursor. Transparent hybrid composite film was obtained in the cured structure of epoxy bridged-polysilsesquioxane nano titanianoxide composites. Q4 (tetra-substituted siloxane bond) silica structure was found in the hybrid of epoxy bridged-polysilsesquioxane with nanosilica when the amount of TEOS added to the epoxy-bridged alkoxysilane reactive precursor was greater than 20phr. The existence of BF3MEA catalyst during curing reaction would help the formation Q4 silica structure from the precursors of epoxy-bridged alkoxysilane with TEOS. The thermal properties and morphologies of the cured epoxy bridged-polysilsesquioxane with nanosilica composite were also affected by adding the BF3MEA curing catalyst. The best thermal stability of the cured epoxy bridged-polysilsesquioxane with nanosilica composite was obtained when 0.2 weight percent of BF3MEA catalyst was used for the precursors of epoxy-bridged alkoxysilane with TEOS. Almost 96% improvement in char. yield was found in the cured epoxy bridged-polysilsesquioxane with nanosilica composite less than 0.2wt% of BF3MEA curing catalyst was used comparing with the pure cured epoxy bridged-polysilsesquioxane. When 0.1wt% of BF3MEA catalyst was used for the thermal curing epoxy-bridged alkoxysilane with TEOS, the best dimensional stability was found. The coefficient of thermal expansion was reduced from 121μm/moC to 60.4μm/moC. and the storage modulus increased from 1Mpa to 6.7Mpa（about 570% enhancement）. The best storage modulus (E’) was obtained when 1.0 weight percent of BF3MEA catalyst was used for the precursors of epoxy-bridged alkoxysilane with TEOS. The TEM spectra of the cured epoxy bridged-polysilsesquioxane with nanosilica composite also showed that BF3MEA curing catalyst exhibited strong effect on the dimension of nanosilica form in the epoxy bridged-polysilsesquioxane matrix. The size of nanosilica formed in the epoxy bridged-polysilsesquioxane matrix changed with the amount of BF3MEA curing catalyst added. Nanosilica with 20nm diameters was found less than 0.1wt% of BF3MEA curing catalyst and the diameter of nanosilica will increase to 200 nm when more than 1wt% of BF3MEA curing catalyst was used.