Abstract
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) n Si8O /(8 − n) −20 − 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 CH3 Si(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) n Si8O /(8 − n) −20 − n (n=2, 3), for both of which three isomers are present, have been estimated.
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Hasegawa, I. Co-hydrolysis products of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions: Part 2 [1]. J Sol-Gel Sci Technol 2, 127–130 (1994). https://doi.org/10.1007/BF00486225
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DOI: https://doi.org/10.1007/BF00486225