NMR studies of sol-gel derived hybrid materials based on triethoxysilylated diethylenetriamine and tetramethoxysilane

Inorganic-organic hybrid materials were prepared by hydrolysis and condensation of triethoxysilylated diethylenetriamine (f-DETA) and tetramethoxysilane (TMOS). The prehydrolysis stage of this f-DETA/TMOS system was monitored by Si-29 NMR spectroscopy. The NMR experiments indicated that f-DETA hydrolyzes and condenses nearly as fast as TMOS at pH 0-1, but lags Far behind the latter at pH similar to 4.2. Gels derived from f-DETA and TMOS were studied using C-13 or Si-29 solid slate NMR spectroscopy. The concentration of the alkoxy groups and the extent of condensation of the T & Q species in the cured gels were estimated. The contents of the Si-OMe group and Si-OEt group wire barely detectable in most water-abundant systems (equivalent ratio of water to alkoxysilane similar to 4.0). However, a significant amount of Si-(OPr)-Pr-i groups was found if the reactant f-DETA was stored at room temperature in solvent 2-propanol for three weeks or longer. The relative composition of each T-z or Q(z) species was estimated for gels prepared in media of different acidity levels and water concentrations and then cured at 125-130 degrees C for 4 h. As the acidity of the medium increased from pH 0-2 to pH 4-5, the extent of condensation of the T species decreased but that of the Q species increased. The hydrolysis of urea groups in f-DETA during the sol-gel process was also evaluated by C-13 solid state NMR spectroscopy. The results indicated that only a very small fraction of urea groups was hydrolyzed during the sol-gel process.