Similarities in the hydrolysis pseudoequilibrium behavior of methyl-substituted ethoxysilanes

S E Rankin, J Sefcik, A V McCormick

Research output: Contribution to journalArticle

13 Citations (Scopus)

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.

LanguageEnglish
Pages3191-3198
Number of pages8
JournalIndustrial and Engineering Chemistry Research
Volume38
Issue number9
DOIs
Publication statusPublished - Sep 1999

Fingerprint

Hydrolysis
Substitution reactions
Equilibrium constants
Silicon
Condensation
Ethanol
Polymerization
Nuclear magnetic resonance
Water

Keywords

  • hydrolysis equilibrium
  • polymerization
  • methylethoxysilanes
  • methyl group

Cite this

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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.",
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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 journalArticle

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T1 - Similarities in the hydrolysis pseudoequilibrium behavior of methyl-substituted ethoxysilanes

AU - Rankin, S E

AU - Sefcik, J

AU - McCormick, A V

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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

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KW - methyl group

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