| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 92 === Epoxy-bridged polyorganosiloxanes have been synthesized by reacting three kinds of aminoalkoxysilanes with di-functional diglycidyl ether of bisphenol-A epoxy resin as precursors, which were thermally cured with or without catalyst to investigate the cured properties of composites.
In this study, three kinds of aminoalkoxysilanes have been used which are 3-aminopropyltriethoxysilane (APTES), 3-aminopropylmethyldiethoxysilane (APMDS), and 3-aminopropyldimethylethoxysilane (APDES). The reaction of amino group with epoxide group is characterized by FTIR. The characteristic peak of epoxide group is 913cm-1, which disappears after 5 hours. Three kinds of precursors used are Reactive Epoxy-APTES precursor, Reactive Epoxy-APMDS precursor and Reactive Epoxy-APDES precursor. The alkoxy groups of precursors were characterized by 1H NMR.
Epoxy-bridged polyorganosiloxanes were cured at 150℃, which was determined by dynamic DSC analysis. Dibutyltindilaurate (DBTDL), tetrabutylamonium hydroxide (NBu4.OH) and boron trifluoride monoethylamine (BF3.MEA) were used; respectively, to study the structures, thermal and mechanical properties of hybrid materials. The bonding structure and degree of condensation of materials were studied by 29Si CP/MAS NMR. The degree of condensation depends on the steric hindrance of reactive functional groups and catalysts. In Epoxy/APTES Bridged Polyorganosiloxane (Epoxy/APTES) system, the degree of condensation is 76.4% without catalyst and 91.4% with BF3.MEA. In Epoxy/APMDS Bridged Polyorganosiloxane (Epoxy/APMDS) system, the degree of condensation is 72.4% without catalyst and 88.0% with BF3.MEA. In Epoxy/APDES Bridged Polyorganosiloxane (Epoxy/APDES) system, the degree of condensation is 77.0% without catalyst and 89.0% with NBu4.OH.
The degradation of composite depends on the degree of condensation. The high bonding energy of Si-O-Si results in the enhancing of the temperature of degradation (Td). Therefore, the higher the degree of condensation it is, the higher the Td it would have. In Epoxy/APTES system, the Td5 is 270.3℃without catalyst and 354.5℃with BF3.MEA (increased 84.2℃). In Epoxy/APMDS system, the Td5 is 347.9℃without catalyst and is 350.8℃with BF3.MEA (increased 3℃). In Epoxy/APDES system, the Td5 is 326.5℃without catalyst and is 343.2℃with NBu4.OH (increased 17℃). The char yeild depends on the content of inorganic component. The hybrid material which contains more inorganic component causes higher char yeild. The char yields of Epoxy/APTES (50.7%), Epoxy/APMDS (42.5%), Epoxy/APDES (16.5%) and Epoxy/DAP (11.3%) are decreasing in order. Furthermore, The Td5 of Epoxy, cured by Diaminopropane (Epoxy/DAP) is 353.6℃.
From TMA studies, it is found that the CTE1 (the coefficient of thermal expansion at the temperature lower than Tg), CTE2 (the coefficient of thermal expansion at the temperature higher than Tg) and the difference ΔCTE (=CTE1-CTE2) of Epoxy/APTES (28, 176 and 148 μm/m℃), Epoxy/APMDS (118, 312 and 194 μm/m℃) and Epoxy/APDES (183, 1981 and 1798 μm/m℃) are increasing in order. Those properties depend on the mobility of the polymer chain which can be obtained by the 13C Solid state NMR. The mobility of Epoxy/APTES is lower than Epoxy/APMDS. The lower molecular mobility causes the lower coefficient of thermal expansion. Hence, in order to reduce the CTE, the T structure is better than D and M structures. The CTE1, CTE2 andΔCTE of Epoxy/DAP are 169, 316 and 147μm/m℃, respectively. Furthermore, the systems which contain inorganic component can reduce the CTE effectively.
The storage modulus (E’) of the systems which contain inorganic component are higher than that of pure epoxy in DMA analysis. At 50℃, the storage modulus of Epoxy/APTES, Epoxy/APMDS, Epoxy/APDES without catalyst and Epoxy/DAP are 1789, 2004, 2374 and 1626 GPa. At 170℃, the storage modulus of Epoxy/APTES, Epoxy/APMDS, Epoxy/APDES without catalyst and Epoxy/DAP are 1175, 147, 9.9 and 6.9 GPa.
The Epoxy/APTES system has unobvious Tg beacuase of the restriction in molecular motion of the T structure. The Tg of D structure, M structure and pure epoxy resin are decreasing in order. Without catalyst, the Tg of Epoxy/APMDS is 151℃, Epoxy/APDES is 90℃ and Epoxy/DAP is 80℃. Hence, the containment of inorganic component of materials would improve the mechanical and thermal properties.
The optical property has been studied by UV/VIS spectra. The transmittances of Epoxy-bridged polyorganosiloxanes in this research are about 100%. From the SEM microphotographs, it was found that the domains of Si-O-Si are smaller than 100 nm and well-dispersed in composite materials.
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