Co-hydrolysis products of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions: Part 2 [1]

²⁹Si NMR peaks due to species with the double four-membered ring siloxane backbone composed of both Si(O^–)_4/2 and CH₃Si(O^–)_3/2 units, (CH₃)_nSi₈O_{20 – n}^{/(8 – n) –}(n=1–3), formed by co-hydrolysis of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions in methanol have been assigned. It has been found that ²⁹Si NMR peaks due to Si(OSi)₃(O^–) units shift to lower frequencies by replacement of the adjacent Si(O^–)_4/2 units by CH₃Si(O^–)_3/2 units, in other words, with increasing m value in Si[OSi(O^–)₃]_{3 – m}[OSi(CH₃) (O^–)₂]_m(O^–) (m=0–2). Peaks from CH₃Si(OSi)₃ units in the species have also appeared as separated due to the kind of neighbor structural units. On the basis of the assignments, positions of CH₃Si(O^–)_3/2 units in the cubic octameric siloxane framework of (CH₃)_nSi₈O_{20 – n}^{/(8 – n) –}(n=2, 3), for both of which three isomers are present, have been estimated.