29 Si NMR sensitivity enhancement methods for the quantitative study of organosilicate hydrolysis and condensation
Quantitative kinetic studies of silicon sol–gel chemistry have proven difficult in the past because the analytical methods currently available are often incapable of providing the requisite temporal resolution or structural information. In the case of 29Si NMR spectroscopy, low isotopic abundance, a small, negative magnetogyric ratio, and long relaxation times contribute to experimental difficulty. Typically this can be overcome through the use of paramagnetic relaxation agents, but we find at neutral pH that the relaxation agents Cr(acac)3 and MnCl2 influence reaction rates. In an effort to avoid the use of potentially reactive relaxation agents, we investigate the quantitative accuracy of the polarization transfer pulse sequence, 29Si RINEPT+ (Refocused Insensitive Nuclei by Polarization Transfer). Due to signal enhancement and shorter acquisition time, RINEPT+ holds promise for use in the study of silicon reaction kinetics when methylated organosilicate starting compounds are used.