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Enzyme-mediated Synthesis of Silsesquioxanes

“…Because each acquired spectrum is the average of multiple scans, the area under each resonance, and consequently the relative proportion of each silane are likely to be underestimated. This method of analysis suffers from being unable to detect transient species such as the single and double hydrolysis products, as well as being unable to differentiate cyclic oligomers which may overlap with the dimerization products [22].…”

“…Knight et al have extensively characterized, through the use of 29 Si COSY NMR, the silicates that are formed during the polymerization of isotopically enriched sodium silicate solutions [21]. The acid-catalyzed sol-gel processing of MeTMOS in ethanol [22], acetone-d 6 , or acetonitrile [23], and the uncatalyzed processing of PhTMOS in a methanol-water system have also been examined using 29 Si NMR [24]. The hydrolysis and condensation of MeTMOS in ethanol allowed for the reaction coordinate to be partitioned into discrete phases.…”

“…The hydrolysis and condensation of MeTMOS in ethanol allowed for the reaction coordinate to be partitioned into discrete phases. Early in the reaction monomer-monomer condensation dominated compared to later in the reaction coordinate when monomer-oligomer and oligomer-oligomer condensations and ring formation were prominent [22]. The model presented by Smith suggests that hydrolysis of MeTMOS, which is first order in substrate, and the condensation of partially hydrolyzed MeTMOS, have competitive rates.…”

New insights on organosilane oligomerization mechanisms using ESI-MS and 29Si NMR

“…These 29 Si{ 1 H} NMR spectra are very much alike to that reported for the hydrolysis/condensation of methyltriethoxysilane (MTES) under acid conditions, an expected observation since MDES Si-H bond cleavage formally leads to MTES. 43 The ESI(+)-MS spectra at different time intervals for the reaction of MDES at pH = 13 are shown in Fig. 5 along with the 29 Si{ 1 H} NMR spectra.…”

Reaction-induced phase separation of bis(triethoxysilyl)ethane upon sol–gel polymerization in acidic conditions

“…Most of the kinetic studies [9][10][11][12][13][14][15][16] of silane polymerization have focused on identification and characterization of the hydrolyzed monomers and oligomers present in solution well before gelation using 29 Si NMR. Silicon site-specific details extracted from 29 Si NMR provide a high level of information about the state of the system that enables the development and validation of mechanistic models capable of predicting structure and properties of the materials synthesised from their precursors.…”