Study of the effects of progressive changes in alkoxysilane structure on sol-gel reactivity

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Effects of the structure of an alkoxysilane on the early reaction kinetics of sol-gel polymerization are investigated in basic and acidic conditions. Six silanes, including tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), bis(trimethoxysilyl)hethane (BTMSE), bis(trimethoxysilyl)hexane (BTMSH), and bis(trimethoxysilylpropyl)amine (BTMSPA), are selected to examine the effects of progressive changes in the silane's structure. In basic conditions, reactivities of the silanes follow the pairwise trends TEOS ≪TMOS, TMOS > MTMS, MTMS < BTMSE, BTMSE ≫ BTMSH, and BTMSH ≪BTMSPA. Hydrolysis rate coefficients of BTMSE, TMOS, MTMS, and BTMSPA are similar in value and are almost one order of magnitude larger than the coefficients of BTMSH and TEOS. In acidic conditions, the pairwise reactivity trends are TEOS ≈TMOS, TMOS < MTMS, MTMS > BTMSE, BTMSE ≫BTMSH, and BTMSH > BTMSPA. The condensation rate coefficients of BTMSH and BTMPA are much smaller than the others. Theses relationships can be explained mainly on the basis of the expected inductive and steric factors of the silanes. Bulky organics attached to the silane lead to low reactivity in both acidic and basic conditions. A high electron density at silicon leads to a low reactivity in basic conditions but a high reactivity in acidic conditions (pH ∼2.3). Only BTMSPA in basic conditions defies these trends, possibly because of the effects of solvation near the reactive silicon site.

Original languageEnglish
Pages (from-to)22353-22364
Number of pages12
JournalJournal of Physical Chemistry B
Issue number45
StatePublished - Nov 16 2006

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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