A mechanistic investigation of gelation. The sol-gel polymerization of precursors to bridged polysilsesquioxanes

K. J. Shea, D. A. Loy

Research output: Contribution to journalArticle

114 Scopus citations

Abstract

The study of a homologous series of precursors to bridged polysilsesquioxanes has uncovered striking discontinuities in gelation behavior. An investigation of the chemistry during the early stages of the polymerization has provided a molecular basis for these observations. Monomers containing from one to four bridging carbon atoms exhibit a pronounced tendency to undergo rapid intra- or bimolecular cyclization. The cyclic and bicyclic intermediates have been characterized by 29Si NMR spectroscopy, chemical ionization mass spectrometry, and isolation from the reaction solution. These carbosiloxanes are local thermodynamic sinks that produce kinetic bottlenecks in the production of high-molecular-weight silsesquioxanes. The formation of cyclic carbosiloxanes results in slowing or in some cases completely shutting down, gelation. An additional finding is that the cyclic structures are incorporated intact into the final xerogel.

Original languageEnglish (US)
Pages (from-to)707-716
Number of pages10
JournalAccounts of Chemical Research
Volume34
Issue number9
DOIs
StatePublished - Oct 3 2001
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)

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