where Cy ) c-C 6 H 11 ) and two POSS-siloxane copolymers [Cy 8 Si 8 O 11 -(OSiMe 2 ) n O-] (n ) 1, oligomer average 5.4) has been studied in argon, nitrogen, and under vacuum from 30 to 1000 °C. Product gases were analyzed by TGA-FTIR and mass spectroscopy. Analysis of the chars was conducted using cross-polarized (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-siloxane copolymers underwent a complex depolymerization-decomposition process. For the copolymer [Cy 8 Si 8 O 11 -(OSiMe 2 ) 5.4 O-] this process included the evolution of cyclic dimethylsiloxanes at 400 °C, cyclohexyl hydrocarbons from 450 to 550 °C, and H 2 liberation from 700 to 1000 °C. Loss of the silsesquioxane "cage" structure occurred upon heating from 450-650 °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.

43) Analogous to those in the ' n r * states of ketones, studied via the circular polarization of the fluorescence, see: Schippers, P. H.; Dekkers, H. P. J. M. Chem. Phys. Lett. 1982.88, 512-516. Dekkers, H. P. J. M.; Moraal, P. F. InAbstract: The first Raman spectra of the allyl radical have been obtained. The intensities of the observed Raman spectra indicate excited-state dynamics consistent with a disrotary photoisomerization of the allyl radical to form a cyclopropyl radical. Prior to this work, direct examination of the photoisomerization pathway was not possible due to limitations of the techniques applied. The ground-state vibrational frequencies observed are found to be in excellent agreement with recent theoretical calculations suggesting a reassignment of the literature infrared frequencies. This work demonstrates that resonance Raman spectroscopy is a powerful method for examination of gas-phase free radicals.

The utility of resonance Raman spectroscopy as an analytical method is studied for application to multicomponent sooting flames. Far-ultraviolet resonance Raman spectra of benzene and trichloroethylene in methane diffusion flames have been obtained. The feasibility of flame temperature determination has been demonstrated for the benzene/methane flame. Resonance enhancement provides the sensitivity and selectivity required to detect low concentrations of aromatics and chlorinated hydrocarbons, in contrast to conventional spontaneous Raman spectroscopy, which suffers from low sensitivity and interference from laser-induced fluorescence of polycyclic aromatic hydrocarbons (PAHs).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.