Polymerization of Hydrolysis Products of Methyltriethoxysilane in Aqueous Solutions

Abstract

The structure and distribution of chemical species of hydrolysis and polycondensation products of methyltriethoxysilane in aqueous solutions containing sodium ions have been studied with the trimethylsilylation technique and by 29Si n. m. r. spectros copy. 11 trimethylsilylated derivatives of the products were obtained from the solutions. The recovery of methyltrisilanol (CH3Si(OH)3) was much higher than that of the monosilicic acid in an aqueous sodium silicate solution at the same Si con centration and the same sodium ion-to-silicon molar ratio, suggesting that the polymerization of silicate anions is easier than that of hydrolysis products of methyltriethoxysilane in aqueous solutions. On the basis of the distribution, assignment of 29Si n. m. r. peaks corresponding to low-molecular weight species formed from methyltriethoxysilane has been discussed. [Received March 6, 1990; Accepted April 13, 1990] Key-words: Methyltriethoxysilane, Hydrolysis, Polymerization, Trimethylsilylation, 29Si n. m. r. spectroscopy IntroductionTrifunctional alkoxysilanes, R1Si(OR2)3, where R1 is an alkyl or aryl group and R2 is an alkyl group, have been used as raw materials for preparation of polyhedral or ladder-like organyl silsesquioxanes.1)-4) Recently, they are also noted as starting materials for producing ceramics, such as silica fibers and silicon carbide powders through the sol-gel processing.5)-8) Since the structures would affect the properties of precur sors and resultant materials, it is necessary to investigate structures of hydrolysis and polycon densation products of trifunctional silanes.It is known that the polymerization of silicate anions in aqueous solutions is affected by various factors, such as the SiO2 concentration, the nature of coexisting cations, the cation-to-silica molar ratio, the pH and the temperature. So far, trimethylsilylation9)-13) and 29Si n. m. r. spectros copy14)-17) have successfully been utilized to in vestigate the structure and distribution of silicate species in solutions. It is expected that these methods would be applicable to the study on hydrolysis and polycondensation products of tri functional alkoxysilanes present in solutions as well.In this study, methyltriethoxysilane (CH3Si (OC2H5)3) has been selected as a trifunctional alkoxysilane in order to obtain basic information on the structure and distribution of the hydrolysis and polycondensation products in aqueous solu tions containing sodium ions. First, the structure and distribution have been investigated with the trimethylsilylation technique combined with gas liquid and gel permeation chromatographies. It was demonstrated that trimethylsilylation by the method of Lentz was adaptable to the investiga tion on species formed by hydrolysis and polymerization of methyltriethoxysilane in solu tions.18) Then, on the basis of the trimethylsilyl ation study, assignment of signals on 29Si n. m. r. spectra of the solutions has been discussed. Although assignment of the signals to each structure unit of methylsilsesquioxanes has been ...

Impact of Silanization on the Structure, Dispersion Properties, and Biodegradability of Nanocellulose as a Nanocomposite Filler

“…Hence, in addition to the R 1 side chain, a T 1 silicon atom has one siloxane (Si–O–Si) bridge and two Si–O–R bridges; a T 2 silicon atom has two Si–O–Si bridges and one S–O–R bridge; and a T 3 silicon atom has three Si–O–Si bridges and zero Si–O–R bridges. The T 1 silicon atoms produce 29 Si peak shifts between −44 and −49 ppm; T 2 silicon atoms result in peaks around −53 to −57 ppm; and T 3 silicon atoms present peak shifts near −68 ppm. − …”

Investigation of hydrolysis and condensation of methyltriethoxysilane in aqueous systems

“…29 Si NMR is an extremely useful technique applied to study hydrolysis and polycondensation of alkoxysilanes [28][29][30][31][32][33]. Thus we have employed a high-resolution 29 Si NMR in our investigation of hydrolysis methyltriethoxysilane and subsequent condensation processes taking place in aqueous emulsion of methyltriethoxysilane, in order to understand a composition of the emulsion and the final process of hydrophobization.…”

“…Some hydrolysis products of organoalkoxysilanes were analyzed and characterized in the past [24,25] by such techniques as IR [26], gas chromatography-mass spectroscopy and 29 Si NMR [27][28][29].…”