Polycondensation behavior of methyltrimethoxysilane studied by NMR spectroscopy

Microwave versus Conventional Heating in the Grafting of Alkyltrimethoxysilanes onto Silica Particles

“…The chemical shift of the methyl groups is progressively higher as the condensation degree (number of siloxane bonds) of the involved silane moieties increases, that is, on going from T 1 to T 3 silyl species. The reported values for the condensation of MTMS on its own (MTMS autocondensation hereafter) range from −8.5 to −4.5 ppm; a comparison between these values and those found in this work indicates that an additional downfield shift of the methyl signal is promoted by the grafting of the silane onto the silica. Hence, the components at high chemical shift (> −4.5 ppm) which appear in Figure are to be associated with T 3 structures and with silane moieties grafted onto the silica.…”

“…The methyl signals are clearly the envelope of several components. A rough deconvolution of the signal can provide at least six different components in each spectrum, what is supported by the literature . The chemical shift of the methyl groups is progressively higher as the condensation degree (number of siloxane bonds) of the involved silane moieties increases, that is, on going from T 1 to T 3 silyl species.…”

“…This is a direct consequence of the presence of nonhydrolyzed methoxy groups in the grafted organic layer, as can be seen in the 13 C CP/MAS NMR spectra reported in Figure . The signal at 49−50 ppm in the 13 C NMR spectra is commonly ascribed to the residual nonhydrolyzed methoxy groups, whereas that peaking at around −5 ppm is due to the methyl groups directly attached to the silicon atoms . The spectra show that the highest amount of nonhydrolyzed methoxy groups is found in the sample RX-M-120, with the rest of the samples containing variable but similar amounts of methoxy groups.…”

“…To help the interpretation of the grafted layer structure, a comparison between the data in Figure and the kinetic study of the MTMS autocondensation published by other authors ,, is performed in the following paragraphs. According to these authors, initially the two dominant species in the reaction medium are the monomer itself, which quickly disappears, and the rapidly formed dimers.…”

Kinetic study of methyltriethoxysilane (MTES) hydrolysis by FTIR spectroscopy under different temperatures and solvents

“…There were mainly three reasons. Firstly, there was strong exchange reaction when an alcohol solvent was used with an alkoxy group different from the alkoxy groups of the silane [27]. In this Fig.…”