Unusual chain configuration of main-chain liquid crystal polyesters having Y-shaped mesogens in nematic phase
Unusual chain configuration of main-chain liquid crystal polyesters having Y-shaped mesogens in nematic phase
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DOI：
10.1016/j.polymer.2011.10.047
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发表时间：
2011-11
期刊：
影响因子：
4.6
通讯作者：
M. Tokita;Kazuya Kato;R. Ishige;Shuhei Okuda;S. Kawauchi;K. Okoshi;Sungmin Kang;J. Watanabe
中科院分区：
文献类型：
--
作者：
M. Tokita;Kazuya Kato;R. Ishige;Shuhei Okuda;S. Kawauchi;K. Okoshi;Sungmin Kang;J. Watanabe
研究了主链液晶Y-n聚酯的向列型液晶，并与常规主链液晶L-n聚酯的向列型液晶进行了比较。Y-N聚酯具有Y形的介晶，支链末端的间隔基连接在一起，作为L-N聚酯柱状介晶的替代。在偏光显微镜下，两种聚酯的向列相都表现出典型的单轴向列相液晶的纹影织构。差示扫描量热法测定的各向同性温度和熵变呈现奇偶振荡现象，Y-n的熵变明显小于L-n的。X-射线衍射和红外二向色性光谱表明，这种低的熵变与Y-n链构型有关，这在MCLC聚合物中是不常见的。单轴向列相结构是由Y形中生体沿指向矢方向排列并绕其主干旋转而形成的，没有任何相关性。通过使用沿指向矢优先放置的间隔物连接这些介元，使我们能够描绘沿着指向矢方向振荡并在垂直于指向矢方向上执行随机行走的链。
The nematic liquid crystals of main-chain liquid crystalline (MCLC) Y-n polyesters were investigated and compared with those of conventional MCLC L-n polyesters. Y-n polyesters have Y-shaped mesogens that are connected by spacers at their branch ends as an alternative to the columitic mesogens of L-n polyesters. The nematic phases of both polyesters under polarized optical microscopy exhibited Schlieren textures that are typical of uniaxial nematic liquid crystals. The isotropization temperature and entropy change estimated by differential scanning calorimetry show odd–even oscillations, which are characteristic of MCLC polymers, and the entropy change of Y-n are significantly smaller than those of L-n. Such a low entropy change is associated with the Y-n chain configuration, which is unusual for MCLC polymers, as revealed by X-ray diffraction and infrared dichroic spectroscopy. The uniaxial nematic structure is formed by Y-shaped mesogens arranging their trunks along the director direction and being rotated about their trunks without any correlation. Connecting these mesogens by using spacers that are placed preferentially along the director enables us to depict the chain that oscillates along the director direction and performs a random walk in the direction perpendicular to the director.