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A Theoretical Study of Silanol Polymerization

Published online by Cambridge University Press:  28 February 2011

Larry W. Burggraf  and
Larry P. Davis
Larry W. Burggraf
Affiliation:
Directorate of Chemical and Atmospheric Sciences, Air Force Office of Scientific Research, Boiling Air Force Base, DC 20332
Larry P. Davis
Affiliation:
Directorate of Chemical and Atmospheric Sciences, Air Force Office of Scientific Research, Boiling Air Force Base, DC 20332
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Abstract

We have applied state-of-the-art semi-empirical molecular orbital methods to a study of the anionic polymerization of silanols to form silica. In particular, we have considered nucleophilic attack on silanols and subsequent reactions of the products. Hydroxide addition proceeds without activation to form five-coordinate silicate anions. Five-coordinate structures can also be formed by oligomerization following the attack of hydroxide on neutral silanols to abstract a proton. These five-coordinate structures are predicted to play a key role as intermediates in the polymerization process. Water can be eliminated from these anions, but with a substantial activation barrier. The activation barrier appears to be lower for the larger, more complex systems. These predictions are consistent with a rapid pre-equilibrium to form dimer anions followed by the slower reaction to form higher oligomers.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 73: Symposium H – Better Ceramics Through Chemistry II , 1986 , 529
Copyright
Copyright © Materials Research Society 1986

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References

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