Octaethoxytrisiloxane, (EtO)3SiOSi(OEt)2OSi(OEt)3 was synthesized and then polymerized in water/alcohol solution in the presence of an acid catalyst. The reaction was monitored with 29Si nuclear magnetic resonance. Using a simple kinetic model, the rate constants of linear and cyclic condensation were estimated by curve-fitting and were compared. No evidence of depolymerization was found, indicating that condensation is irreversible in our conditions. In addition, it was found that the formation of trimeric cyclic species by ring closure is fast and competes effectively with chain extension condensation. These observations are consistent with previous suggestions, but in addition they provide a quantitative measure of selectivity. Quantitative kinetic models for silicon alkoxide sol-gel processes need to account for cyclization at very early stages of the polymerization.
Bibliographical noteFunding Information:
This work was supportedb y a grant from the Office of Naval Researcha ndwith a fellowshipto J.S. from the Center for InterraciaEl ngineering at the University of Minnesota.T he authors gratefullya cknowledghe elpful discussionsw ith ProfessorC .W. Macosko,P rofessorL .E. Scriven, Anshu Gupta and Rich Cairncrossa t the University of Minnesota.
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