Flow magic-angle spinning (MAS) and two-dimensional exchange NMR studies of heterogeneous catalysis and polymer microstructure

Solid-state nuclear magnetic resonance (NMR) spectroscopy is an extremely important technique for the study of the structure, dynamics, and reactions of molecules in the solid state. However, often new techniques need to be developed in order to obtain useful chemical information about these systems. This thesis describes the development of a flow magic-angle spinning (MAS) system for the study of heterogeneous catalysis reactions in situ and the application of multi-dimensional NMR techniques to study the crystalline structure of polylactide as well as the role of stereodefects in the polymer morphology.; A flow variable temperature (VT) MAS NMR probe was developed to study heterogeneous catalysis reactions in situ at temperatures greater than 300°C. The conversion of methanol to gasoline (MTG) range hydrocarbons over zeolite HZSM-5 was used as a model test reaction for investigating the capabilities of the probe under batch and flow conditions. Through a series of one-dimensional (1D) NMR experiments, we found that the equilibrium established in the first step of the MTG reaction differed between batch and flow conditions.; Polylactide (PLA) is a semicrystalline polymer synthesized from lactide which has three stereoisomers: L-(S,S), D-(R,R), and meso-(S,R) lactide. In the crystalline region of poly(L-lactide) (PLLA), the polymer chain forms a 10₃ helix. The 1D 13C cross polarization (CP) MAS NMR spectrum of PLLA has multiple resonances for each carbon, suggesting inequivalent sites within the helix. Several 2D exchange NMR experiments of isotopically labeled PLLA were performed in order to assign the connectivity of the different resonances and to determine the relative torsion angles of the carbonyl groups.; Pure PLLA or poly(D-lactide) (PDLA) can be up to 90% crystalline and 10% amorphous. Incorporation of small amounts of stereodefects into the polymer affects the polymer crystallinity. Through a series of 1D 13C CP/MAS NMR experiments on isotopically labeled and unlabeled polymer samples, we investigated the local environment of these stereodefects. The experiments revealed that stereodefects are incorporated into both the amorphous and crystalline regions of PLA. Finally, the local environment of the stereodefects in the crystalline domain of the polymer was examined using 2D exchange NMR.