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Polymeric Silsesquioxanes: Degree-of-Intramolecular-Condensation Measured by Mass Spectrometry



William E. Wallace, Charles M. Guttman, Joseph M. Antonucci


The degree-of-condensation, defined as the number of residual silanol (SiOH) groups per oligomer, for a variety of silsesquioxane polymers was measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Condensation of SiOH groups out of the silsesquioxane molecule leads to the formation of intramolecular Si-O-Si bridges accompanied by the loss of water. This elimination reaction is easily identified via high resolution time-of-flight mass spectrometry. Various polymeric silsesquioxanes were prepared from the corresponding trialkoxysilanes by hydrolysis-condensation reactions at moderate temperatures (25 C to 65 C) in aqueous acetone with catalytic amounts of formic acid. A decyl-silsesquioxane was found to have the highest degree on condensation with lower degrees found in n-propyl- and in 3-methacryloxypropyl- silsesquioxanes. A propyl silsesquioxane synthesized without a catalyst was found to have the lowest degree-of-condensation of all as well as the lowest overall molecular weight. In all cases the number of intramolecular Si-O-Si bridges per oligomer was found to be a linear function of the number of repeat units in the oligomer. This linear relationship is discussed in light of theories of condensation polymerization.
No. 6


mass spectrometry, polymerization, silsesquioxanes


Wallace, W. , Guttman, C. and Antonucci, J. (2000), Polymeric Silsesquioxanes: Degree-of-Intramolecular-Condensation Measured by Mass Spectrometry, Polymer, [online], (Accessed April 18, 2024)
Created February 29, 2000, Updated October 12, 2021