title: 222 nm Photo-induced radical reactions in silazanes. A combined laser photolysis, EPR, GC-MS and QC Study.
abstract: The initiation mechanism of the VUV-induced conversion of polyorganosilazanes into methyl-Si-O-Si networks was studied by means of model disilazane compounds. A combined experimental approach was chosen to determine the primary radicals and their properties (lifetimes, spectra) as well as the major final products. It was verified that both Si-N and Si-CH(3) cleavage occur in the condensed phase, the former with higher yield. The lifetime of the primary Si- and N-centred radicals in de-oxygenated n-hexane solution is less than </=10 mus. N-centred radicals transform into amines by H abstraction, the availability of weakly bonded H as in the case of tetramethyldisilazane accelerates the reaction considerably. In rigid matrix (frozen solutions) CH(3), silyl radicals and methylene radicals CH(2)R are trapped. In the presence of oxygen, peroxyl radicals are formed and serve as precursors of the subsequent oxidative conversion. Product analysis by GC-MS reveals linear R-(Si-O)(n)- chains rather than branched compounds as the initial products of the oxidative conversion of tetramethyldisilazane. It was shown that reactive silylene intermediates do not play a role in the conversion process. Quantum chemical calculations assist in the interpretation.
authors.affiliation: Leibniz-Institut für Oberflächenmodifizierung, Permoserstrasse 15, D-04318 Leipzig, Germany. wolfgang.knolle@iom-leipzig.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Knolle
authors.forename: Luise
authors.initials: L
authors.lastname: Wennrich
authors.forename: Sergej
authors.initials: S
authors.lastname: Naumov
authors.forename: Konstanze
authors.initials: K
authors.lastname: Czihal
authors.forename: Lutz
authors.initials: L
authors.lastname: Prager
authors.forename: Daniel
authors.initials: D
authors.lastname: Decker
authors.forename: Michael R
authors.initials: MR
authors.lastname: Buchmeiser
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D007834:Lasers; D010782:Photolysis; D011786:Quality Control; D012828:Silicones / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D005609:Free Radicals; D012828:Silicones