IDENTIFICATION AND CHARACTERIZATION OF THE HYDROLYSIS PRODUCTS IN TMOS AND MTMS MONOMERS USING SI-29 NMR AND POLARIZATION TRANSFER TECHNIQUES

High-resolution Si-29 NMR was used to identify and characterize the hy drolysis products of tetramethoxysilane (TMOS) and methyltrimethoxysil ane (MTMS). The identification of the different hydrolysis species was accomplished using the spectral editing properties of the DEPT and IN EPT heteronuclear polarization transfer experiments, Previous resonanc es assignments for the hydrolyzed monomers in TMOS were quickly confir med using these techniques. Unambiguous assignment of the MTMS hydroly sis products is complicated by a small spectral dispersion and the pre sence of two different hydrogen-silicon J couplings in these species. Analytical expressions for the INEPT signal response under multiple he teronuclear J couplings allowed these assignments. It is shown that th e optimal polarization transfer efficiency in TMOS, MTMS and correspon ding hydrolyzed products can only be obtained if the pulse sequence pa rameters are optimized for each species. The temperature dependences o f the Si-29 NMR resonances for the hydrolysis products in TMOS and MTM S were investigated and found to be very similar, with the magnitude a nd sign of the temperature response being dependent on the number of h ydroxyl groups attached to the silicon. For MTMS hydrolysis products t he small Si-29 chemical shift dispersion along with the variation of c hemical shift with temperature and solvent requires that resonance ass ignments be made for each experimental condition.