In the present study, bis(triethoxysilyl)ethane (BTESE) is compared with methyltriethoxysilane (MTES). Their hydrolysis and condensation reactions are monitored in situ by 29Si NMR and FT-IR spectroscopy. Polarization transfer using the DEPT pulse sequence is used to enhance the 29Si NMR sensitivity without requiring a paramagnetic relaxation agent. A mathematical model is developed and solved to determine the rate constants of MTES and BTESE polymerization. The model is applied under conditions where both monomers remain homogeneous throughout the experiment. However, it is found that the polymerization products of BTESE are prone to the loss of NMR signal during the experiments at certain initial concentrations of the monomer. The loss of signal can be attributed to the precursor entering into an environment where fast tumbling cannot occur, most likely due to microphase separation.
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