- Author
- Mantz, R. A. | Jones, P. F. | Chaffee, K. P. | Lichtenhan, J. D. | Gilman, J. W. | Ismail, I. M. K. | Burmeister, M. J.
- Title
- Thermolysis of Polyhedral Oligomeric Silsesquioxane (POSS) Macromers and POSS-Siloxane Copolymers.
- Coporate
- Phillips Laboratory, Edwards AFB, CA National Institute of Standards and Technology, Gaithersburg, MD Hughes STX
- Journal
- Chemistry of Materials, Vol. 8, No. 6, 1250-1259, 1996
- Keywords
- pyrolysis | siloxanes | monomers | vapor phases
- Abstract
- The pyrolysis of four polyhedral oligomeric silsesquioxane (POSS) macromers, Cy₈-Si₈O11(OH)₂, Cy₈Si₈O11(OSiMe₃)₂, Cy₆Si₆O₉, and Cy₈Si₈O12 (where Cy = c-C₆H11) and two POSS-siloxane copolymers [Cy₈Si₈O11-(OSiMe₂)nO-] (n = 1, oligomer average 5.4) has been studied in argon, nitrogen, and under vacuum from 30 to 1000 deg C. Product gases were analyzed by TGA-FTIR and mass spectroscopy. Analysis of the chars was conducted using cross-polyarized (CP) and magic angle spinning (MAS) NMR spectroscopy, X-ray diffraction, density measurements, and gas adsorption analysis. All of the POSS macromers showed a propensity toward sublimation, while the POSS-silioxane copolymers underwent a complex depolymerization-decomposition process. For the copolymer [Cy₈Si₈O11-(OSiMe₂)5.4O-] this process included the evolution of cyclic dimethylsiloxanes at 400 deg C, cyclohexyl hydrocarbons from 450 to 550 deg C, and H₂ liberation from 700 to 1000 deg C. Loss of the silsesquioxane "cage" structure occurred upon heating from 450-650 deg C and after the evolution of most of the pyrolysis gases. Changes in both char porosity and density accompanied the structural rearrangements. The activation energies for pyrolysis under argon or nitrogen was 56 ± 9 kcal/mol and for oxidation in air was 20 ± 4 kcal/mol.