Abstract
By considering a range of conditions where the condensation time scale significantly exceeds that of hydrolysis, we are able to quantify by Si-29 NMR the alkoxide hydrolysis equilibrium constants of silicon sites with varying degrees of ethoxy, siloxy, and methyl group substitution during polymerization of methylethoxysilanes in ethanol/water mixtures. Although there is a strong emphasis in existing literature on differences in hydrolysis behavior with such substitutions, we find a surprising lack of variation in these coefficients: all are near 15 +/- 6. This implies that in practice, while hydrolysis rates may vary with substitution, differences in hydrolysis pseudoequilibrium behavior may often be negligible. Surprisingly, we also find that, even under alkaline conditions, sites with exactly one uncondensed group reach hydrolysis pseudoequilibrium, although other sites in the same solution do not.
| Language | English |
|---|---|
| Pages | 3191-3198 |
| Number of pages | 8 |
| Journal | Industrial and Engineering Chemistry Research |
| Volume | 38 |
| Issue number | 9 |
| DOIs | |
| Publication status | Published - Sep 1999 |
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Keywords
- hydrolysis equilibrium
- polymerization
- methylethoxysilanes
- methyl group
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Similarities in the hydrolysis pseudoequilibrium behavior of methyl-substituted ethoxysilanes. / Rankin, S E ; Sefcik, J ; McCormick, A V .
In: Industrial and Engineering Chemistry Research, Vol. 38, No. 9, 09.1999, p. 3191-3198.Research output: Contribution to journal › Article
TY - JOUR
T1 - Similarities in the hydrolysis pseudoequilibrium behavior of methyl-substituted ethoxysilanes
AU - Rankin, S E
AU - Sefcik, J
AU - McCormick, A V
PY - 1999/9
Y1 - 1999/9
N2 - By considering a range of conditions where the condensation time scale significantly exceeds that of hydrolysis, we are able to quantify by Si-29 NMR the alkoxide hydrolysis equilibrium constants of silicon sites with varying degrees of ethoxy, siloxy, and methyl group substitution during polymerization of methylethoxysilanes in ethanol/water mixtures. Although there is a strong emphasis in existing literature on differences in hydrolysis behavior with such substitutions, we find a surprising lack of variation in these coefficients: all are near 15 +/- 6. This implies that in practice, while hydrolysis rates may vary with substitution, differences in hydrolysis pseudoequilibrium behavior may often be negligible. Surprisingly, we also find that, even under alkaline conditions, sites with exactly one uncondensed group reach hydrolysis pseudoequilibrium, although other sites in the same solution do not.
AB - By considering a range of conditions where the condensation time scale significantly exceeds that of hydrolysis, we are able to quantify by Si-29 NMR the alkoxide hydrolysis equilibrium constants of silicon sites with varying degrees of ethoxy, siloxy, and methyl group substitution during polymerization of methylethoxysilanes in ethanol/water mixtures. Although there is a strong emphasis in existing literature on differences in hydrolysis behavior with such substitutions, we find a surprising lack of variation in these coefficients: all are near 15 +/- 6. This implies that in practice, while hydrolysis rates may vary with substitution, differences in hydrolysis pseudoequilibrium behavior may often be negligible. Surprisingly, we also find that, even under alkaline conditions, sites with exactly one uncondensed group reach hydrolysis pseudoequilibrium, although other sites in the same solution do not.
KW - hydrolysis equilibrium
KW - polymerization
KW - methylethoxysilanes
KW - methyl group
U2 - 10.1021/ie990027v
DO - 10.1021/ie990027v
M3 - Article
VL - 38
SP - 3191
EP - 3198
JO - Industrial and Engineering Chemistry Research
T2 - Industrial and Engineering Chemistry Research
JF - Industrial and Engineering Chemistry Research
SN - 0888-5885
IS - 9
ER -