SI-29 NMR-STUDY OF THE HYDROLYSIS AND CONDENSATION OF EPOXS SOL-GEL SOLUTION

The hydrolysis and condensation process of organically substituted alk oxy silanes can be studied at the molecular level by using Si-29 nucle ar magnetic resonance (NMR). The sol-gel process of EPOXS (an epoxysil ane: 3-glycidyloxypropyltrimethoxysilane) has been followed with the r eaction time by the Si-29 NMR spectra. At least 15 distinct Si-29 reso nances were recorded in the present system studied, and most of them h ave been assigned to the corresponding structure groups. The relative content of the structure groups was obtained by integration of the Si- 29 NMR peaks. The study shows that under our experimental conditions t he hydrolysis of EPOXS is very fast and complete when more than the st oicheiometric amount of water is added. Water concentration also influ ences the distribution of the structural groups. Ester exchange reacti on can be clearly observed in the sample containing less water, which occurs concurrently with the hydrolysis reaction.