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Intramolecular Condensation Reactions of α, ω-BIS(Triethoxysilyl) Alkanes. Formation of Cyclic disilsesquioxanes

Published online by Cambridge University Press:  10 February 2011

Douglas A. Loy
Affiliation:
Properties of Organic Materials
Joseph P. Carpenter
Affiliation:
Properties of Organic Materials
Sharon A. Myers
Affiliation:
Properties of Organic Materials
Roger A. Assink
Affiliation:
Properties of Organic Materials
James H. Small
Affiliation:
Organic Materials Processing Departments, Sandia National Laboratories, Albuquerque, NM 87185-1407, daloy@sandia.gov
John Greaves
Affiliation:
Department of Chemistry, University of California Irvine, Irvine, CA 92717-2025
Kenneth J. Shea
Affiliation:
Department of Chemistry, University of California Irvine, Irvine, CA 92717-2025
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Abstract

Under acidic sol-gel polymerization conditions, 1,3-bis(triethoxysilyl)-propane 1 and 1,4-bis(triethoxysilyl)butane 2 were shown to preferentially form cyclic disilsesquioxanes 3 and 4 rather than the expected 1,3-propylene- and 1,4-butylene-bridged polysilsesquioxane gels. Formation of 3 and 4 is driven by a combination of an intramolecular cyclization to six and seven membered rings, and a pronounced reduction in reactivity under acidic conditions as a function of increasing degree of condensation. The ease with which these relatively unreactive cyclic monomers and dimers are formed (under acidic conditions) helps to explain the difficulties in forming gels from 1 and 2. The stability of cyclic disilsesquioxanes was confirmed with the synthesis of 3 and 4 in gram quantities; the cyclic disilsesquioxanes react slowly to give tricyclic dimers containing a thermodynamically stable eight membered siloxane ring. Continued reactions were shown to perserve the cyclic structure, opening up the possiblity of utilizing cyclic disilsesquioxanes as sol-gel monomers. Preliminary polymerization studies with these new, carbohydrate-like monomers revealed the formation of network poly(cyclic disilsesquioxanes) under acidic conditions and polymerization with ring-opening under basic conditions.

Type
Research Article
Copyright
Copyright © Materials Research Society 1996

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References

[1] Review on hydrocarbon-bridged polysilsesquioxanes: Loy, D. A.; Shea, K. J., Chem. Rev. 95, 1431, (1995).CrossRefGoogle Scholar
[2] a) Small, J. H.; Shea, K. J.; Loy, D. A., J. Non Cryst. Solids 160, 234 (1993). b) H. W. Oviatt, Jr.; K. J. Shea; J. H. Small, Chem. Mater. 5, 943 (1993). c) D. A. Loy; G. M. Jamison; B. M. Baugher; E. M. Russick; R. A. Assink; S. Prabakar; K. J. Shea, J. Non Cryst. Solids 186, 44 (1995).CrossRefGoogle Scholar
[3] Sol-gel polymerizations were carried out at 0.4 M monomer concentration. It is significant to note that while bridged triethoxysilanes generally gel with a few hours at this concentration, tetraethoxysilane will not gel until the monomer concentrations is above 1.8 M.Google Scholar
[4] Voronokov, M. G., Lavrent‘yev, V. I., Top. Curr. Chem. 102, 199 (1982).CrossRefGoogle Scholar
[5] a) Englehardt, G.; Jancke, H.; Magi, M.; Pehk, T.; Lippmaa, E., J. Organomet. Chem. 28, 293 (1971). b) D. J. Burton; R. K. Harris; K. Dodgson; C. J. Pellow; J. A. Semlyen, Polymer Commun. 24, 278 (1983).CrossRefGoogle Scholar
[6] Siloxane (Si-O-Si) bond angles were calculated to be 131.86° for 3 and 141.02° for 4 in comparison with a value of 145° for acyclic siloxanes. Calculations were performed using MM2 based models in Chemdraw 3D Plus, Cambridge Scientific Computing.Google Scholar
[7] Hydrolysis of organotriethoxysilanes under identical conditions gave rise to three discrete peaks downfield from the monomer (T0) resonance due to the three possible hydrolysis products. Condensation reactions generate three groups of peaks upfield relative to T0 representing silsesquioxanes with one (T1), two (T2) and three (T3) siloxane bonds.Google Scholar
[8] 29Si CP MAS NMR T1-T3 signals are broader and farther downfield than the corresponding solution 29Si NMR signals due to contributions from hydrolyzed and cyclic siloxanes. See: Kelts, L. W.; Effinger, N. J.; Melpolder, S. M., J. Non Cryst. Solids 83, 353 (1986).CrossRefGoogle Scholar

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Intramolecular Condensation Reactions of α, ω-BIS(Triethoxysilyl) Alkanes. Formation of Cyclic disilsesquioxanes
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