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Characterization of Olefin Polymerization Reactions Using Dissolution Dynamic Nuclear Polarization
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NNuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool with widespread applications in all areas of synthetic chemistry including polymer chemistry. High-resolution solution-state NMR not only provides accurate qualitative and quantitative information on the chemical structure from small molecules to macromolecules, but it is also capable of determining detailed local structure, i.e., microstructure, which is not accessible by any other techniques. However, the major drawback of NMR is its low sensitivity. Dissolution Dynamic Nuclear Polarization (D-DNP), a hyperpolarization technique, provides a several thousand-fold enhancement of NMR signals. When combined with stopped-flow techniques, time scales on the order of seconds can be accessed by real-time NMR spectroscopy. We demonstrate that polymer microstructures and reaction kinetics can be determined simultaneously using this method. Examples used for this purpose are metallocene-catalyzed polymerization and ring-opening metathesis polymerization (ROMP). We discuss model equations used for describing the time evolution of hyperpolarized monomer signals and for determining rate constants of initiation, propagation, and deactivation. The results can be used to distinguish mechanisms leading to living polymerization, polymerization subject to deactivation, or to slow initiation. When applying the D-DNP NMR method with a copolymerization reaction, cross-propagation and self-propagation rate constants are calculated using comonomer signals detected simultaneously in ^13C spectra. These rate constants further determine the copolymer composition. Finally, we demonstrate the use of real-time NMR to measure the polarization transfer between hyperpolarized small molecules and polymers in an equilibrium chemical system. The improved signal-to-noise ratio provided by hyperpolarization allows for site specific characterization of intermolecular interactions in a single-scan measurement.
SubjectNuclear Magnetic Resonance
Dynamic Nuclear Polarization
Chen, Chia-Hsiu (2018). Characterization of Olefin Polymerization Reactions Using Dissolution Dynamic Nuclear Polarization. Doctoral dissertation, Texas A & M University. Available electronically from