Liquid Crystallinity of Thermotropic Liquid crystal Polymers Studied by Two-Dimensional Poralized Infrared Spectroscopy and X-ray Diffraction Correlation Spectroscopy

热致液晶聚合物R_1、R_2、R_3和R_4的主链上含有苯基，侧链上含有小分子液晶。在其侧链末端附加了柔性烷氧基-O(CH_2)_5-CH_3，通过降低其熔点实现液晶状态。本研究的目的是利用二维红外光谱和X射线衍射相关光谱研究四种液晶聚合物R_1、R_2、R_3、R_4的结构与液晶性之间的关系。从X-射线衍射图中发现，R_1、R_2、R_3和R_4为向列型液晶，不仅介元，而且主链都是定向的，侧链与主链相吻合。方向不是二维的，而是三维的。这不是简单的问题，而是复杂的问题。DSC结果表明，R_1、R_2、R_3和R_4不是纯向列型液晶，而是部分表面型液晶。变温红外光谱研究发现，该化合物中存在两种C=O基团，侧链中存在C-O键周围的构象变化。由R_1、R_2、R_3和R_4的变温红外光谱计算的非同步光谱表明，侧链的取向温度高于主链。这一结果也得到了随温度变化的X射线衍射测量的证实。

Thermotropic liquid crystal polymers, R_1,R_2,R_3, and R_4, which contain a phenyl group in the main chain, have a rigid backbone and in their side chains a low molecular weight liquid crystal is incorporated. At the end of their side chains a flexible alkoxy group -O(CH_2)_5-CH_3 is attached to realize liquid crystalline states by reducing their melting points. The purpose of the present study was to explore the relation between the structure and the liquid crystallinity of the four kinds of liquid crystalline polymers, R_1,R_2,R_3,R_4 by using two-dimensional infrared spectroscopy and x-ray diffraction correlation spectroscopy.First of all, the phase transition temperatures of R_1,R_2,R_3, and R_4 were determined by measuring differential scanning calorimetry (DSC) and polarized microscopy. It was found from x-ray diffraction patterns that R_1,R_2,R_3, and R_4 are nematic liquid crystals and that not only the mesogen but also the main chain are oriented with the side chains being fitted inside the other. The orientation is not two dimensional but three dimensional. it is not simple one but complicated one. The DSC results revealed that R_1,R_2,R_3, and R_4 are not pure nematic liquid crystal but partly smetic liquid crystal. It was found from temperature-dependent infrared spectroscopic study that there are two kinds of C=O groups and conformational change around the C-O bond occurs in the side chain. An asynchronous spectrum calculated from the temperature-dependent infrared spectra of R_1,R_2,R_3, and R_4 elucidated that the side chain is oriented at higher temperature than the main chain. This result was also confirmed by the temperature-dependent x-ray diffraction measurements.