Cyclization phenomena in the sol-gel polymerization of {alpha},{omega}-bis(triethoxysilyl)alkanes and incorporation of the cyclic structures into network silsesquioxane polymers

Journal Article · Wed Jun 16 04:00:00 EDT 1999 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja982751v· OSTI ID:684323

Loy, D A; Carpenter, J P; Alam, T M; Shaltout, R ^[1]; Dorhout, P K ^[2]; Greaves, J; Shea, K J ^[3]; Small, J H ^[4]

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1. Sandia National Labs., Albuquerque, NM (United States)
2. Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemistry
3. Univ. of California, Irvine, CA (United States). Dept. of Chemistry
4. Los Alamos National Lab., NM (United States). Polymers and Coatings Group

Intramolecular cyclizations during acid-catalyzed sol-gel polymerizations of {alpha},{omega}-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 {sup 29}Si 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), 1,4-bis(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 {sup 29}Si 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.

• Research Organization: Sandia National Laboratory
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 684323
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 23 Vol. 121; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ALKANES
CYCLIZATION
DIMERS
ETHOXY RADICALS
ORGANIC SILICON COMPOUNDS
POLYMERIZATION
SOL-GEL PROCESS