含矽氧連結基之氫鍵香蕉型液晶雙體與主鏈型高分子之研究

Abstract

本實驗以Mitsunobu coupling、hydrosilylation、esterification，合成出含二或三個矽氧連結基在中心和不同芳香環在兩側末端的五種質子予體雙頭酸，這些質子予體雙頭酸與質子受體單吡啶、雙吡啶以氫鍵混掺方式各別形成雙體與主鏈型高分子之氫鍵香蕉型液晶，並以POM、IR、TGA、DSC、XRD及三角波光電量對其物性與光電性質作探討。 結果顯示增加矽氧基能使軟鏈段更柔軟，變換芳香環種類使液晶基更剛硬，氫鍵彎曲形結構不對稱，有利於增廣液晶相範圍；此外,氫鍵能增強氫鍵結構的熱穩定性；反鐵電極化層列相C(SmCPAF)與鐵電極化層列相C(SmCPF)分別在二與三個矽氧連結基的雙體與主鏈型高分子之氫鍵香蕉型液晶被觀察到；高自發極化值(Ps)能藉由增加芳香環數目與引入不對稱彎曲形結構而獲得。

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.