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29Si NMR spectrometry has been used to determine the number molecular weight distribution of polymerization degrees of a system of oligomers formed in the sol-gel polycondensation of tetraethoxysilane (TEOS). On the basis of identification of the oligomers, monitoring of the concentration changes during the initial phase of the sol-gel polycondensation, and from the deviations observed between the experimentally determined number molecular weight distribution of polymerization degrees and the Flory-Stockmayer model it has been proved that cyclization represents a significant process in the acid-catalyzed polycondensation with substoichiometric amount of water (ratio of amounts TEOS/H2O = 1 : 1). The cyclization becomes important at the moment when the reaction mixture contains increased amounts of the linear tetramer and pentamer. The cyclization products form a basis for formation of polycyclic, highly condensed building units whose gradual aggregation produces the gel.

The determination of alcohols by 19F NMR spectroscopy making use of their reaction with hexafluoroacetone giving rise to hemiacetals was studied on butanols. The calibration curve method and the internal standard method were used and the results were mutually compared. The effects of some experimental conditions, viz. the sample preparation procedure, concentration, spectrometer setting, and electronic integration, were investigated; the conditions, particularly the concentrations, proved to have a statistically significant effect on the results of determination. For the internal standard method, the standard deviation was 0.061 in the concentration region 0.032-0.74 mol l-1. The method was applied to a determination of alcohols in the distillation residue from an oxo synthesis.

The polycondensation of tetraethoxysilane (TEOS) catalyzed with dibutylbis[1-oxo(dodecyl)oxy]stannane (dibutyltin dilaurate, DBTDL) has been investigated with the help of 1H and 29Si NMR spectrometry and quasi elastic light scattering (QELS). It has been found that in contrast to the acid catalyzed polycondensation the siloxane chain grows in linear and branched way, the proportion of cyclization reactions being slight. The rate of chain growth is relatively high, which is indicated by the impossibility to detect the presence of shorter oligomers in the reaction mixture by means of 29Si NMR. The found rate constant of polycondensation of TEOS catalyzed with DBTDL is k = 0.052 dm6 min-1 mol-1. From the determined condensation degree at the gelation point (0.20-0.35) and the ratio of consumed amount of ethoxysilane units to the consumed amount of monomer at the gelation point (0.49-0.69) it follows that the gel is predominantly formed by cross-linking of branched macromolecules, the reaction mixture containing no distinct proportions of polycyclic and highly condensed structural units. The density of network of the gel formed is relatively low, which was proved by 29Si CP/MAS NMR spectra of the solid gels. Investigation of QELS of the reaction mixture showed that the relatively large particles, microgels, were formed practically immediately after the reaction had started. The presence of such particles in the reaction mixture of acid catalyzed polycondensation of TEOS was not proved.

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