Molecular Aspects of Mesophase Formation of Polymer Liquid Crystals As Revealed by ^2H NMR Analyzes and PVT Measurements

我们的兴趣是研究各向异性环境中柔性链的构象和热力学作用。主链型液晶将柔性链段作为连接两个介晶核的单元。从积累的实验数据来看，这种液晶在向列相-各向同性相界面上的转变熵除以间隔基数时几乎保持不变。因此，我们的研究从含有间隔基的二聚体和三聚体模型化合物开始，如-O(CH_2)_NO-，n=9和10。这些液晶化合物可以用精确的结构合成。这些液晶的二元混合物使我们能够研究分子量分布的影响。我们的研究成果得到了为期两年的Monbusho基金的支持，其结果总结如下：1.^2H核磁共振分析提供了一种解释给定混合物各组分的取向有序参数的技术。当二聚体或定时剂LC溶解在单体LC中时，序参数…在主链型LC中，嵌合单元与间隔基之间的键角对决定嵌合核心的取向顺序起着重要的作用。状态方程分析(Flory表达式)表明，二聚体和三聚体LCS的自由体积约为NI转变点上方各向同性状态下核心体积的20%。NI转变时的体积变化约为10-20%。结合~2H核磁共振和PVT的测量表明，间隔基构象的变化是导致NI和CN跃迁的潜熵的主要原因。这一观察结果立即表明，主链LCS中所涉及的间隔基的立体化学组成有效地决定了系统的各种热力学性质。沿着这条线，手性间隔体的计算机设计正在我们实验室进行。其中一些化合物已经合成并进行了测试。较少

Our interest is to study the conformation and the thermodynamic role of flexible chains involved in an anisotropic environment. Mainchain-type liquid crystals (LC) involve flexible segments as a unit connecting two mesogenic cores. From the accumulated experimental data, transition entropies of such LCs at the nematic-isotropic interphase remain nearly invariant when divided by the number of spacers. Our study thus started from dimer and trimer model compounds having a spacer such as -O (CH_2)_nO- with n=9 and 10. These LCs can be synthesized with a precise constitution. Binary mixtures of these LCs allow us to investigate the effect of molecular weight distribution. The results of our research, supported by the Monbusho grant for a two-year period, are summarized as follows :1. The ^2H NMR analysis provided a technique to elucidate the orientational order parameter of the individual components of a given mixture. When dimer or timer LCs were dissolved in a monomer LC,the order paramet … More er of the mosogenic units of the former were found to be lower than those of the monomeric LC.In the mainchain-type LCs, bond angles conneting the mosogenic units to the spacer play an important role in determining the orientational order of the mosogenic core.2. The equation of state analysis (Flory's expression) indicated that the free volumes of the dimer and trimer LCs are about 20% of the core volume in the isotropic state just above the NI transition point. The volume changes at the NI transition were found to be about 10-20%.3. Combined use of the ^2H NMR and PVT measurements revealed that variation of the spacer conformation is largely responsible for the latent entropy at the NI as well as CN transitions. This observation immediately suggests that the stereochemical constitution of the spacer involved in the mainchain LCs effectively determines various thermodynamic properties of the system. Along this line, computer design of chiral-spacers is in progress in our laboratory. Some of them have been synthesized and tested. Less