The effects of sodium ion on hydrolysis and condensation of diethoxydimethylsilane

The effect of sodium ion on hydrolysis and condensation of diethoxydimethylsilane (DEDMS) was investigated by Si-29 NMR spectroscopy. Discussed were the possibility of Si-O-Na linkage through sol-gel processes and the difference of structure for the solutions between with and without sodium ions. Si-29 NMR signals shifted with time for the solution containing NaOH. The shift depended on both OH- and Na+ ion concentration of the solution and would be attributed to the exchange reaction between sodium ion and proton of Si-OH. The exchange was observed for the solution with more than pH = 13.0. When sodium ion was added into the solution mixed with DEDMS and H2O, the proportion of cyclic trimer and tetramer decreased and the molecular weight of condensed species are also reduced, because the sodium ion played the role of a terminator.