Elucidation of Polymer Conformation, Phase Structure, and Dynamics by Multidimensional Solid-State NMR

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9703916 Schmidt-Rohr In this research program, multidimensional nuclear magnetic resonance (NMR) techniques are developed and applied to elucidate the conformations and motions of functional groups in solid polymers and relate them to macroscopic materials properties. The proposed NMR techniques for characterizing segmental conformations in unoriented polymers, such as amorphous polymers and polypeptides, are based on measuring the relative orientations of adjacent segments by correlating anisotropic NMR couplings (dipolar and chemical-shift anisotropies). The torsion-angle informatiol is extracted from characteristic intensity patterns in the resulting 2D or 3D spectra. Eventually, in a 3D spectrum, 2D chemical-shift correlation patterns will be separated by dipolar couplings. The torsion-angle distributions in various PET samples, polystyrenes, and other polymers will be characterized. Double-quantum NMR techniques for measuring the torsion angles and in peptides have been demonstrated and will be applied to solid polypeptide materials. Structure and mobility on a larger scale, e.g. in phase-separating polymer blends or at the crystalline-amorphous interface, will be investigated by spin-diffusion NMR. In the area of molecular dynamics of solid polymers, multidimensional exchange NMR methods that were introduced in part by this PI have elucidated relaxations in polymers, which influence many macroscopic materials properties. New exchange NMR techniques will be developed, aiming, for instance, at detecting small-amplitude or localized motions. Motional processes, such as helical jumps, will be exploited for obtaining structural information, e.g. to characterize polymer chain folds. The length scale of motional heterogeneities in polymers above the glass transition will be determined based on spatial information from spin diffusion. %%%% In this research program, solid polymers such as engineering plastics and advanced biomaterials are investigated on a mole cular level by novel nuclear magnetic resonance (NMR) techniques. The insight into molecular structures and motions, which are related to mechanical properties such as toughness or creep, will ultimately help industry in the development of improved polymer materials. Students from three departments will be instructed about modern NMR in theory and practice, while several graduate students will be trained to use the latest multidimensional NMR techniques in polymer research. ***