STUDIES ON THE LASER DEGRADATION OF THE CHCL3 SOLUTION OF POLYSILANE

In this paper, the XeCl excimer laser was used to irradiate the CHCl3 solution of polymethylphenethylsilane (PMPES) and that of poly(dimethy lsilane-co-methylphenethylsilane) (PDM-MPES). The laser energy absorbe d by the polysilane macromolecules was measured, the gel permeation ch romatography molecular weights of the polysilane macromolecules both b efore and after irradiation were determined, and their corresponding a pparent quantum yields under the irradiation were calculated. The appa rent quantum yield of laser degradation of the CHCl3 solution of PMPES is two orders of magnitude larger than that of the CHCl3 solution of PDM-MPES, indicating that the spatial obstruction of the substituents attached to the polysilane chains has great effect on its apparent qua ntum yield of laser degradation. For the polysilane photodegradation u nder a rather low laser energy, with the increase of the laser energy absorbed by the polysilane macromolecules, the average molecular weigh t after irradiation decreases gradually while the average scissions pe r macromolecule and the apparent quantum yield increase. The concentra tion of the CHCl3 solution of polysilane has only small effect on its apparent quantum yield of laser degradation. According to the X-ray ph otoelectron spectroscopy analysis, the CHCl3 solvent is involved in th e photoreaction and combined into the dissociated product. In light of the references, it is preliminarily proposed that the laser degradati on of the CHCl3 solution of polysilane may result from the comprehensi ve action of such factors as homolytic cleavage, silylene extrusion, c hain cleavage by reductive elimination, the radical chain transfer pro cess, the fluorescence quenching of polysilane by CHCl3, etc. (C) 1997 John Wiley & Sons, Inc.