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（LC）由柔性链段作为一个单元连接两个介晶核。从累积的实验数据来看，在向列-各向同性间相，这种LCs的跃迁熵除以间隔层的数量几乎保持不变。因此，我们的研究从二聚体和三聚体模型化合物开始，这些模型化合物具有n=9和10的间隔物，如- o (CH_2)_nO-。这些lc可以用精确的结构合成。这些lc的二元混合物使我们能够研究分子量分布的影响。我们的研究得到了为期两年的Monbusho基金的支持，研究结果总结如下：1。^2H核磁共振分析提供了一种阐明给定混合物中各个组分的取向顺序参数的技术。当二聚体或定时器LC溶解于单体LC中时，前者的序参量明显低于单体LC。在主链型烃源岩中，将生烃单元与间隔段连接起来的键角对决定生烃岩心的取向顺序起着重要作用。状态方程分析（Flory’s表达式）表明，二聚体和三聚体LCs在NI过渡点以上各向同性状态下的自由体积约为核心体积的20%。NI转变时的体积变化约为10-20%。结合使用^2H核磁共振和PVT测量表明，间隔层构象的变化是NI和CN跃迁的潜在熵的主要原因。这一观察结果立即表明，参与主链LCs的间隔剂的立体化学组成有效地决定了体系的各种热力学性质。沿着这条路线，我们实验室正在进行手性间隔剂的计算机设计。其中一些已经被合成并进行了测试。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