Type of Document Dissertation Author Mrse, Anthony Adrian Author's Email Address firstname.lastname@example.org URN etd-1018101-000938 Title Analysis of Inorganic Materials Using Advanced NMR and NQR Techniques Degree Doctor of Philosophy (Ph.D.) Department Chemistry Advisory Committee
Advisor Name Title Leslie Butler Committee Chair Britt Thomas Committee Member Erwin Poliakoff Committee Member Robert Strongin Committee Member Kerry Dooley Dean's Representative Keywords
- flame retardant
- nuclear quadrupole resonance
- spin lattice relaxation in the rotating frame
- nuclear magnetic resonance
- bridging methyl
Date of Defense 2001-09-25 Availability unrestricted Abstract
Several advanced solid-state nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) techniques have been applied to inorganic materials of commercial interest. The specific techniques applied to each system were chosen to solve specific obstacles which impeded the flow of industrial science.
First, the dispersion of brominated flame retardants in polymers is monitored using pulsed 81Br NQR (nuclear quadrupole resonance) techniques. The NQR spectrometer consists of a homemade NMR console and an automatically tuned loop-gap resonator probe. The two factors which affect the 81Br NQR transition frequencies of brominated aromatics are: electron-donating and withdrawing substituents on the ring and bromine intermolecular contacts.
The crystal structure of isobutyl aluminoxane and high field 27Al MAS NMR spectra, acquired at spinning speeds of 35 kHz, are presented. The structure contains both bridging hydrides and three-coordinate aluminum sites. Geometry optimized restricted Hartree-Fock (RHF) calculations of an idealized structure yield Cq and h in close agreement with experiment.
Very high field, field swept 27Al NMR spectra of two forms of MAO, MAO(solid) and MAO(gel) were recorded. In the field swept experiment, Bo is swept while B1 remains constant. Using a sweep technique facilitates the observation of exceedingly large line-widths. Simulations of the MAO(gel) line-shape indicate the upper limits of Cq to be 22.5 MHz (calculated using h = 0). Additionally, the spectra of MAO and related compounds were studied by 27Al MAS NMR spectroscopy using a high homogeneity 19.6 T magnet and spinning speed up to 35 kHz. Successful determination of spectral parameters in these cases awaits the availability of even higher magnetic fields and spinning rates in excess of 35 kHz.
Last, to measure the abundance of bridging methyl groups in MAO, 1H NMR spin-lattice relaxations in the rotating frame, T1ñ, investigations of methyl group motions were observed. MAO is found to exhibit a biexponential decay. The T1ñ method serves as a qualitative measure of bridging methyl group abundance and MAO(gel) is shown to have nearly twice as many bridging methyl sites as MAO(solid).
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