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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 ,
Joseph P. Carpenter ,
Sharon A. Myers ,
Roger A. Assink ,
James H. Small ,
John Greaves  and
Kenneth J. Shea
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
Information
MRS Online Proceedings Library (OPL) , Volume 435: Symposium V – Better Ceramics Through Chemistry VII , 1996 , 33
Copyright
Copyright © Materials Research Society 1996

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References

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