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Abstract
The cross polarization spin dynamics of solids were studied, and methods were found to manipulate them to increase the resolution in CP/MAS spectra. Inversion recovery cross polarization (IRCP) experiments were used to study the morphology of semicrystalline polymers. In both polyethylene and poly(oxymethylene), IRCP cleanly resolves the crystalline and amorphous components, and allows their spectral features to be measured separately. The level of crystallinity was also determined. A generalization of IRCP, tailored cross polarization (TCP), was designed to further increase the resolution in CP/MAS experiments. It is shown that a spectrum representing those resonances in a compound which have a given cross polarization time, T$\sb{\rm CH}$, may be observed separately from all other resonances.
The methods of calculating motionally averaged powder patterns for stationary samples is reviewed, and an approach is suggested which greatly decreases the amount of CPU time necessary for the calculation. A connectivity matrix is constructed which contains the interconnections in chemical shift caused by the motion. The indices of the matrix represent the chemical shifts, and the value of the matrix element gives the population of all species contributing to this element. The line shape calculation proceeds as suggested by others, however use is made of the fact that the line shape calculation for all matrix elements M$\sb{\rm 1,m}$ where $\mid$1 $-$ m$\mid$ = c, c is a constant, are identical.
Background resonances are often observed in Bloch decay spectra in solids. These generally arise from Teflon or other materials which are used in the probe construction. It is demonstrated that pulse sequences which select homogeneous regions of the r.f. field (e.g. DEPTH) suppress these resonances since they originate from well outside of the coil. The use of a DEPTH pulse in T$\sb1$ measurements is also demonstrated.
High resolution solid state NMR techniques were employed to investigate the chemistry of methylamine (MA) on zeolite Y at room temperature. The results are consistent with MA undergoing a series of deamination reactions to form ethylamine followed by isopropylamine, which then looses hydrogen to form the imine.
The construction of a 1.4T solid state spectrometer capable of performing these studies is also described.