Sol-gel formation of heteropolysiloxanes from diethylphosphatoethyltriethoxysilane and tetraethoxysilane

Abstract

Transparent monolithic gels were prepared from the cohydrolysis of diethylphosphatoethyltriethoxysilane (OC2H5)2P(O)CH2CH2Si(OC2H5)3 (SiP) and tetraethoxysilane Si(OC2H5)4 (TEOS) in various ratios, under acidic conditions. The hydrolysis and initial polycondensation of SiP were studied by high-resolution 29Si-NMR. Based on signal intensities, singnals due to the following oligomers were identified: R(OH)2SiOSi(OH)(R)OSi(OH)2, R(OH)2SiOSi(OH)2, R(OH)(OEt)SiOSi(OH)2R, R(OH)(OEt)SiOSi(OH)2R, R(OH)2SiOSi(OH)(R)OSi(OH)2R and [R(OH)SiO-]-3. 29Si NMR Quantitative analysis was performed on SiP–TEOS mixtures during the hydrolysis-condensation reactions and on the final gels. This provided information on the formation of the gels molecular structure. © 1996 John Wiley & Sons, Inc.