Cyclization phenomena in the sol-gel polymerization of α,ω- bis(triethoxysilyl)alkanes and incorporation of the cyclic structures into network silsesquioxane polymers

Douglas A Loy, Joseph P. Carpenter, Todd M. Alam, Raef Shaltout, Peter K. Dorhout, John Greaves, James H. Small, Kenneth J. Shea

Research output: Contribution to journalArticle

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Abstract

Intramolecular cyclizations during acid-catalyzed sol-gel polymerizations of α,ω-bis(triethoxysilyl)alkanes substantially lengthen gel times for monomers with ethylene (1), propylene (2), and butylene (3) bridging groups. These cyclization reactions were found, using mass spectrometry and 29Si NMR spectroscopy, to lead preferentially to monomeric and dimeric products based on six- and seven-membered disilsesquioxane rings. 1,2-Bis(triethoxysilyl)ethane (1) reacts under acidic conditions to give a bicyclic dimer (5) that is composed of two annelated seven-membered rings. Under the same conditions, 1,3-bis(triethoxysilyl)propane (2), 1,4bis(triethoxysilyl)butane (3), and Z-1,4-bis(triethoxysilyl)but-2-ene (10) undergo an intramolecular condensation reaction to give the six- and seven- membered cyclic disilsesquioxanes 6, 7, and 11. Subsequently, these cyclic monomers slowly react to form the tricyclic dimers 8, 9, and 12. With NaOH as polymerization catalyst, these cyclic silsesquioxanes readily reacted to afford gels that were shown by CP MAS 29Si NMR and infrared spectroscopies to retain some cyclic structures. Comparison of the porosity and microstructure of xerogels prepared from the cyclic monomers 6 and 7 with those of gels prepared directly from their acyclic precursors 2 and 3 indicates that the final pore structure of the xerogels is markedly dependent on the nature of the precursor. In addition, despite the fact that the monomeric cyclic disilsesquioxane species cannot be isolated from 1-3 under basic conditions due to their rapid rate of gelation, spectroscopic techniques also detected the presence of the cyclic structures in the resulting polymeric gels.

Original languageEnglish (US)
Pages (from-to)5413-5425
Number of pages13
JournalJournal of the American Chemical Society
Volume121
Issue number23
DOIs
StatePublished - Jun 16 1999
Externally publishedYes

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Alkanes
Cyclization
Polymethyl Methacrylate
Polymerization
Paraffins
Sol-gels
Polymers
Gels
Xerogels
Monomers
Dimers
Nuclear magnetic resonance spectroscopy
Magnetic Resonance Spectroscopy
Propane
Condensation reactions
Butane
Gelation
Pore structure
Ethane
Porosity

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Cyclization phenomena in the sol-gel polymerization of α,ω- bis(triethoxysilyl)alkanes and incorporation of the cyclic structures into network silsesquioxane polymers. / Loy, Douglas A; Carpenter, Joseph P.; Alam, Todd M.; Shaltout, Raef; Dorhout, Peter K.; Greaves, John; Small, James H.; Shea, Kenneth J.

In: Journal of the American Chemical Society, Vol. 121, No. 23, 16.06.1999, p. 5413-5425.

Research output: Contribution to journalArticle

Loy, Douglas A ; Carpenter, Joseph P. ; Alam, Todd M. ; Shaltout, Raef ; Dorhout, Peter K. ; Greaves, John ; Small, James H. ; Shea, Kenneth J. / Cyclization phenomena in the sol-gel polymerization of α,ω- bis(triethoxysilyl)alkanes and incorporation of the cyclic structures into network silsesquioxane polymers. In: Journal of the American Chemical Society. 1999 ; Vol. 121, No. 23. pp. 5413-5425.
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abstract = "Intramolecular cyclizations during acid-catalyzed sol-gel polymerizations of α,ω-bis(triethoxysilyl)alkanes substantially lengthen gel times for monomers with ethylene (1), propylene (2), and butylene (3) bridging groups. These cyclization reactions were found, using mass spectrometry and 29Si NMR spectroscopy, to lead preferentially to monomeric and dimeric products based on six- and seven-membered disilsesquioxane rings. 1,2-Bis(triethoxysilyl)ethane (1) reacts under acidic conditions to give a bicyclic dimer (5) that is composed of two annelated seven-membered rings. Under the same conditions, 1,3-bis(triethoxysilyl)propane (2), 1,4bis(triethoxysilyl)butane (3), and Z-1,4-bis(triethoxysilyl)but-2-ene (10) undergo an intramolecular condensation reaction to give the six- and seven- membered cyclic disilsesquioxanes 6, 7, and 11. Subsequently, these cyclic monomers slowly react to form the tricyclic dimers 8, 9, and 12. With NaOH as polymerization catalyst, these cyclic silsesquioxanes readily reacted to afford gels that were shown by CP MAS 29Si NMR and infrared spectroscopies to retain some cyclic structures. Comparison of the porosity and microstructure of xerogels prepared from the cyclic monomers 6 and 7 with those of gels prepared directly from their acyclic precursors 2 and 3 indicates that the final pore structure of the xerogels is markedly dependent on the nature of the precursor. In addition, despite the fact that the monomeric cyclic disilsesquioxane species cannot be isolated from 1-3 under basic conditions due to their rapid rate of gelation, spectroscopic techniques also detected the presence of the cyclic structures in the resulting polymeric gels.",
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AU - Loy, Douglas A

AU - Carpenter, Joseph P.

AU - Alam, Todd M.

AU - Shaltout, Raef

AU - Dorhout, Peter K.

AU - Greaves, John

AU - Small, James H.

AU - Shea, Kenneth J.

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AB - Intramolecular cyclizations during acid-catalyzed sol-gel polymerizations of α,ω-bis(triethoxysilyl)alkanes substantially lengthen gel times for monomers with ethylene (1), propylene (2), and butylene (3) bridging groups. These cyclization reactions were found, using mass spectrometry and 29Si NMR spectroscopy, to lead preferentially to monomeric and dimeric products based on six- and seven-membered disilsesquioxane rings. 1,2-Bis(triethoxysilyl)ethane (1) reacts under acidic conditions to give a bicyclic dimer (5) that is composed of two annelated seven-membered rings. Under the same conditions, 1,3-bis(triethoxysilyl)propane (2), 1,4bis(triethoxysilyl)butane (3), and Z-1,4-bis(triethoxysilyl)but-2-ene (10) undergo an intramolecular condensation reaction to give the six- and seven- membered cyclic disilsesquioxanes 6, 7, and 11. Subsequently, these cyclic monomers slowly react to form the tricyclic dimers 8, 9, and 12. With NaOH as polymerization catalyst, these cyclic silsesquioxanes readily reacted to afford gels that were shown by CP MAS 29Si NMR and infrared spectroscopies to retain some cyclic structures. Comparison of the porosity and microstructure of xerogels prepared from the cyclic monomers 6 and 7 with those of gels prepared directly from their acyclic precursors 2 and 3 indicates that the final pore structure of the xerogels is markedly dependent on the nature of the precursor. In addition, despite the fact that the monomeric cyclic disilsesquioxane species cannot be isolated from 1-3 under basic conditions due to their rapid rate of gelation, spectroscopic techniques also detected the presence of the cyclic structures in the resulting polymeric gels.

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