Proton Multiple Quantum NMR Studies of Space and End Chain Conformation in Liquid Crystals

各向异性相中柔性链的构象和有序化问题近年来引起了人们的广泛关注。这项工作的大部分动机是希望了解芳香族核心上的烷基链是如何影响介晶相性质和稳定性的。液晶聚合物作为高强度纤维和涂层的可能来源以及它们在电光器件中的可能应用，也一直是研究的主题。尽管具有刚性主链的聚合物一般不会形成液晶相，也不会在熔融成同形相之前分解，但在聚合物主链中引入柔性间隔链将把中间相转变温度降低到热分解范围以下。氢核磁共振谱已成为探索端链和间隔链的微观结构和动力学，以及测试向列相中链有序化模型的主要工具。Drobny教授提出了一种利用多重量子光谱研究向列相和低温中间相中间隔物和端链有序性的方法。由多量子谱得到的质子-质子和质子-碳偶极耦合直接计算构象几率和有序张量元，而不是链有序和构象的测试模型。

The problem of the conformation and ordering of flexible chains in anisotropic phases has attracted a good deal of attention in recent years. The motivation of most of this work is a desire to understand the manner in which alkyl chains pendant to aromatic cores influence mesomorphic phase properties and stability. Liquid crystal polymers have also been the subject of research as possible sources of high tensile strength fibers and coatings, and for their possible applications in electro-optic devices. Although polymers with rigid backbones do not generally form liquid crystalline phases, or decompose before melting into memorphic phases, the introduction of flexible spacer chains into the polymer backbone will lower mesophase transition temperatures to below the range of thermal decomposition. Deuterium NMR spectroscopy has been the principal tool for probing the microscopic structure and dynamics of end and spacer chains, and for testing models of chain ordering in nematic phases. Professor Drobny proposes an approach to studying spacer and end chain ordering in the nematic phase and in several in low temperature mesophases using multiple quantum spectroscopy. Rather than test models of chain ordering and conformation, conformational probabilities and order tensor elements will be directly calculated from proton-proton and proton-carbon dipolar couplings obtained from multiple quantum spectra.