Nonclassical Pathways for Silsesquioxane Growth

Abstract

The mechanism of silsesquioxane growth is studied with an insertion mechanism analogous to the one previously proposed for fullerene growth. Different from previous work, the possibility of the involvement of larger rings with (SiO)7 size in cages of hydridosilsesquioxanes Si n O3 n /2H n is investigated. Such a nonclassical pathway is calculated for the growth of Si30O45H30 via Si32O48H32 to Si34O51H34. The MSINDO method is used to determine the transition structures and intermediates. It is found that nonclassical pathways are equally preferable as classical pathways involving cages with (SiO)5 and (SiO)6 rings only.

Theoretical Study of the Reaction Mechanism and Role of Water Clusters in the Gas-Phase Hydrolysis of SiCl4

“…However, as before, the mechanism was not validated by the quantitative comparison with experimental data. Jug and Gloriozov 15,16 proposed an alternative mechanism of siloxane growth which is clearly applicable to the further stages of hydrolysis, because the breaking of the first Si-Cl bond can be considered as an initial step of this mechanism. Jug and coworkers 17 also investigated the various radical processes probably occurring during the high-temperature synthesis of SiO 2 from SiCl 4 and O 2 .…”

“…Since the 1990s, there have been a number of theoretical studies of the mechanism of siloxane formation. − First, Kudo and Gordon 11,12 investigated the reactions of SiHCl 3 and SiH 4 - x (OH) x with water at the Si−Cl hydrolysis step and at further condensation steps. They estimated the activation energies and found that the energy of activation at both the primary hydrolysis and activation steps can be significantly lowered by the coordination of additional water molecules to the transition structures.…”