Magnetic Resonance Studies of Order and Dynamics in Liquid- Crystalline Polymers

9420458弗莱德曼这个项目专注于对液晶聚合物的有序性和动力学进行核磁共振研究。这些新材料在几种结构和电子应用中发挥着特殊的作用。它们的主要特征是对形成液晶溶液的强烈亲和力，以及在进入固态时保持这些溶液排列的能力。这种组合使得产生具有宝贵的机械、热和非线性光学性能的高度有序的大分子材料成为可能。在这些聚合物的实际应用方面的进一步进展与了解化学结构和外部因素(如流场)控制其动态和取向的方式密切相关。使用最先进的液晶和固相多维核磁共振以及基于梯度的磁共振显微镜方法来探索这些方面。这些实验广泛依赖于一种专门的技术，其目的是在分子和超分子水平上表征局部各向异性环境。它们包括使用高温动态角度组件研究熔融热致性，使用可变角旋转探头进行定序和重新取向的固相分析，以及使用流变学成像仪器研究热致性流体中的流动。使用这些技术，将有可能探索热致液晶中的局部介晶有序性如何取决于化学组成；这些系统在冷却成玻璃时有多少液晶有序性被保留；固相链动力学如何影响这些聚合物玻璃的排列以及它们的确切性质是什么；以及不同类型的流动和扩散如何赋予液晶聚合物溶液的净各向异性。这些实验的一个重要方面是对13C自旋的自然丰度观测的依赖，这是一种对所研究的样品的类型或来源没有任何先决条件的方法。因此，要分析的材料包括具有高熔点的均聚酯、商用热致共聚物、液晶和无规聚合物的复杂分子混合物，以及腐蚀性溶致溶液。%所有这些都是高度相关的系统，对它们的更好理解应该对它们的实际应用产生重大影响。

9420458 Frydman This project focuses on nuclear magnetic resonance investigation of order and dynamics in liquid-crystalline polymers. These new materials play special roles in several structural and electronic applications. Their main characteristics are a strong affinity towards the formation of liquid-crystalline solutions, and an ability to retain these solution arrangements upon going into the solid state. This combination makes possible the generation of highly ordered macromolecular materials with valuable mechanical, thermal and non-linear optical properties. Further advances in the practical utilization of these polymers are intimately linked to understanding the ways in which chemical structures and external factors such as flow fields, can control their dynamics and orientations. These aspects are explored using state-of-the-art multidimensional nuclear magnetic resonance in both the liquid-crystalline and the solid phase, as well as gradient-based magnetic resonance microscopy methods. These experiments rely extensively on a specialized technology whose purpose is the characterization of local anisotropic environments at molecular and supramolecular levels. They involve the use of high-temperature dynamic-angle assemblies for studying molten thermotropics, of variable-angle spinning probeheads for solid-phase analyses of order and reorientations, and of rheo-imaging instrumentation for the investigation of flow in lyotropics. Using these techniques it will be possible to probe how local mesomorphic order in thermotropic liquid- crystals depends on chemical composition; how much of the liquid-crystalline order of these systems is preserved upon cooling them into glasses; how solid-phase chain dynamics affect the alignment of these polymeric glasses and what is their exact nature; and how different types of flow and diffusion impart a net anisotropy of solutions of liquid- crystalline polymers. An important aspect of these experiments is the ir reliance on the natural-abundance observation of 13C spins, a method that imposes no preconditions on the type or origin of the samples under study. Thus, the materials to be analyzed include homopolyesters with high melting temperatures, commercial thermotropic copolymers, complex molecular blends of liquid- crystalline and random polymers, and corrosive lyotropic solutions. %%% All these are highly relevant systems, whose better understanding should have a significant impact on their practical application.