Importance of cyclization during the condensation of hydrolyzed alkoxysilanes

Hydrolyzed alkoxysilanes exhibit decreasing condensation reactivity as the connectivity of a reacting site increases. However, until recently cyclization was neglected when quantifying this effect. We apply two kinetic models, one neglecting cyclization, the other accounting for cyclization (using in part the illustrated scheme), to Si-29 NMR data of hydrolyzed alkylethoxysilanes. We show that the true negative first shell substitution effect is even more severe than previously thought when neglecting cyclization.