Nuclear-magnetic-resonance study of silica gelation kinetics.

The gelation of a silicon alkoxide has been investigated by 29 Si NMR. The degree of reaction, which is given by the analysis of the magic-angle spinning spectra, is shown to saturate at the degree of condensation c≃0.84 at long times. The gel fraction is obtained from the decomposition of the static spectra into a solidlike component arising from the infinite static network (the gel) and a liquidlike component coming from the coexisting finite mobile polymers (the sol)