| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 91 === The sol-gel technology was used to prepare organic/inorganic nanocomposites containing silicon and phosphorus. The flame-retardants could be successfully incorparated into the network of hybrids. It will lead to the increasing of the flame retardance and thermal properties. This thesis is divided into the following three parts：
The first part of the thesis is to synthesize the epoxy nanocomposites. Organic-inorganic hybrids were prepared using DGEBA type epoxy and tetraethoxysilane via sol-gel process. In order to improve the compability between the organic and inorganic phases, coupling agent was used to modify the DGEBA type epoxy. Applying the sol-gel technique, the silicon and phosphorus could be successfully incorparated into the network of hybrids. It will lead to the increasing of the flame retardance. FTIR and 29Si NMR were used to characterize the structure of the hybrids. Results revealed it formed the network structure. SEM and Si mapping showed that the hybrids were nanocomposites. The LOIs of pure epoxy and epoxy nanocomposites indicate that epoxy nanocomposites possess better flame retardance. The limiting oxygen indices (LOI) of pure epoxy and modified epoxy hybrid are 24 and 32, respectively. TGA data show the thermal stability of epoxy nanocomposites at high temperature are better than those of the pure epoxy. Four analytical methods, Van Krevelen, Horowitz-Metzger, Coats-Redfern, and MacCallum-Tanner methods were used to obtain the kinetic parameters of thermal degradation for comparison. It was found that the value of E for modified epoxy hybrid(116kJ/mol) is smaller than that of pure epoxy(282kJ/mol).
The second part of the thesis is to synthesize the phenolic/silica nanocomposites. The novel phenolic/silica hybrid ceramers were synthesized by sol-gel process. FTIR and 29Si NMR revealed that network structures were formed Results revealed that Q4, Q3, T3 are the major microstructures. The particles were uniformly dispersed throughout the polymer matrix with sizes below 100nm. SEM, TEM and Si mapping revealed the hybrids were nanocomposites. The char yields of the hybrids increased with increasing TEOS content. The char yields of the hybrids increase with increasing TEOS contents. Td5 (the degradation temperature of 5% weight loss) of the hybrid containing 20% TEOS content was 2900C. As the TEOS content increases to 80%, Td5 of the hybrid is 3120C. TEOS inorganic components enhance the heat stability of hybrids. L.O.I. (value increased from 32 to 44) and the UL-94 test（UL-94 class was promoted V1 to V0） revealed that the hybrid ceramer possesses excellent flame retardance.
The third part of the thesis is to synthesize the polysilsesquioxanes. The first series of the polysilsesquioxanes is ladder-like phosphorus-containing polysilsesquioxanes. The second series of the polysilsesquioxanes is the bridged polysilsesquioxanes. The Td10 (the temperature of degradation at which weight loss is 10%) of ladder-like phosphorus-containing polysilsesquioxanes is 423℃. The char yield of polysilsesquioxanes is 34 wt% at 800℃. From DSC curves, the glass transition temperature of ladder-like phosphorus-containing polysilsesquioxanes is not clear enough. It reveals that the ladder-like macromolecular backbone is so rigid that the movement of the segmental chain is restricted. From the kinetics analysis of thermal degradation, the activation energy of thermal degradation is 187 kJ/mol by the Kissinger's method. However, by the Ozawa's method, the activation energy of thermal degradation generally increases with increasing of conversion. The average activation energy calculated from Ozawa method is 209 kJ/mol. The morphology confirms the ladder-like polysilsesquioxanes were uniformly dispersed at a molecular level and the sizes of the polysilsesquioxanes particles were less than 100 nm. The UV/VIS spectra measured for ladder-like polysilsesquioxanes reveal excellent optical transparency. For bridged polysilsesquioxanes, Td10 of Urea-PSSQ、1,6-PSSQ and 1,4-PSSQ are 412℃、507℃ and 581℃, respectively. The char yields of Urea-PSSQ、1,6-PSSQ and 1,4-PSSQ are 54.69%、70.55% and 81.19%, respectively. From these results, it may conclude that these materials possess excellent thermal stability. The UV/VIS spectra measured for bridged polysilsesquioxanes reveal excellent optical transparency.
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