Study of Hydrogen-Bonded Banana-Shaped LC Dimers and Main-Chain Polymers Containing Siloxane Linking Groups
|關鍵字:||矽氧基;彎曲型硬核;香蕉型;氫鍵;主鏈型高分子;雙體;Siloxane;Bent Core;Banana-shaped;Hydrogen-Bonded;Main-Chain Polymers;Dimers|
In this study, five kinds of diacid proton donors containing two or three siloxane linking groups in the center and variou aromatic rings at both terminals were synthesized using Mitsunobu coupling, hydrosilylation, and esterification. These diacid donors were mixed with pyridyl and bipyridyl acceptors, respectively, to form H-bonded banana-shaped dimers and main-chain polymers. The physical and electro-optical properties were characterized by polarizing optical microscopy (POM), infrared spectrometer (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and electro-optical experiments. It was found that increasing the length of siloxane units and the rigidity of aromatic rings would brooden the mesogenic ranges. As the H-bonded bent-core structures were asymmetric, it showed wider ranges of mesogenic phases. In addition, hydrogen bonds also enhanced the thermal stability of the H-bonded structures. The anti-ferroelectric polar smectic C (SmC PAF) and ferroelectric polar smectic C (SmC PF) phases were individually observed in these H-bonded dimers and main-chain polymers bearing two and three siloxane units. The high spontaneous polarization (Ps) values were obtained by increasing the number of aromatic rings, and by introducing the asymmetric bent-core structures.
|Appears in Collections:||Thesis|
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