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

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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.