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主链上含苯基，主链为刚性结构，侧链为低分子量液晶。在它们的侧链末端连接一个柔性的烷氧基-O（CH_2）_5-CH_3，通过降低它们的熔点实现液晶态。本文用二维红外光谱和X射线衍射相关光谱研究了四种液晶聚合物R_1，R_2，R_3，R_4的结构与液晶性的关系，首先测定了R_1，R_2，R_3，用差示扫描量热法（DSC）和偏光显微镜测定R_4。X-射线衍射分析表明，R_1，R_2，R_3，R_4均为双相液晶，不仅液晶基元而且主链都是侧链相互嵌配的取向。定向不是二维的而是三维的。这不是一个简单的问题，而是一个复杂的问题。DSC结果表明，R_1，R_2，R_3，R_4不是纯的双相液晶，而是部分的同相液晶。变温红外光谱研究发现，侧链中存在两种C=O基团，且在C-O键附近发生构象变化。由R_1，R_2，R_3，R_4的变温红外光谱计算得到的非同步谱图说明侧链的取向温度高于主链。这一结果也证实了温度依赖的X射线衍射测量。

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.