Laser Desorption Mass Spectrometry of Polysilanes

Abstract

Laser ablation of a variety of polysilanes at 308 nm using fluences of 150–250 mJ/cm2 per pulse, well above the photoablation threshold, is a photothermal process and yields products identical with those obtained in vacuum pyrolysis with a CO2 laser. Unsaturated hydrocarbon products characteristic of the side chains have been identified unequivocally. Silicon-containing products have not been identified individually, and it is proposed that they are a mixture of cyclic carbosilanes, mostly containing no more than two or three silicon atoms linked to each other. A reaction mechanism for the ablation process is proposed and involves no previously unknown reaction steps. The results demonstrate that laser-desorption mass spectrometry is a good analytical tool for the identification of side chains in this class of polymers and suggest that laser-desorption gas chromatography or even simple pyrolysis gas chromatography will be useful. Due to the high volatility of the hydrocarbons, the presence of even quite long side chains on the polymer backbone need not be a source of much concern in practical applications of the photoablation process. © 1989, American Chemical Society. All rights reserved.