| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 98 === poly(diethylsiloxane) (PDES) is a flexible main-chain isotropic polymer which has columnar mesophase depending on molecular weight. High molecular weight PDES has been shown to crystallize into two different modifications: α and β phase PDES. Preferably kinetic α phase is a monoclinic packing and the thermodynamically more stable β phase has formed tetragonal lattice. A third crystalline modification has been reported for low molecular weight PDES. This modification, designated γ PDES, was found to closely resemble the tetragonal β modification. This study is employed by a parallel plate rheometer to compare the viscosities of mesophase PDES and PDMS under the changes in temperature. An apparent increase in viscosity and dynamic viscoelastic properties were found when PDES was in the isotropic temperature range. It was attributed to the formation of viscoplastic body caused by pseudo crosslinking. In contrast, PDMS demonstrates common shear thinning behavior and its viscoelastic properties are unchanged.
Moreover, PDES is performed by differential scanning calorimetry (DSC) and polarizing optical microscope (POM) and parallel plate rheometer (Physica MCR 301) to conform that mesophase temperature range is between 7℃and 17℃. The viscosity and dynamic viscoelastic properties decreased with the climbing percentage of shear strain due to the loosening of pesudo crosslinking networks. The phenomena of amorphous PDES and PDMS do not occur.
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