Vacuum Ultraviolet Photolysis of Polydimethylsiloxane: Gas Yields and Energy Transfer

摘要

A polydimethylsiloxane polymer was irradiated with 1470 A and 1236 A radiation, and the quantum yields of the gas products were determined. Analysis of the data indicates that the breaking of the Si-CH3 bond is the most probable reaction occurring at both wavelengths. For surface irradiations, C2H6, CH4, and H2 are primary products, while for immersion irradiations, only CH4 and H2 are produced. The differences in the two types of experiments are ascribed to the competition between bimolecular CH3 combination and radical abstraction reactions; the surface irradiation favors the former mechanism. A mixed methyl-phenyl polymer ((CH3) (phi)2Si-O-Si(CH3)2 - O - Si (CH3) (phi)2) was also irradiated at 1470 A. No C2H6 was found for this polymer. Also solutions of the phenyl-containing polymer in the polydimethylsiloxane were irradiated. It was found that the gas yields were reduced by both radical addition to the phenyl groups as well as intermolecular energy transfer between the two polymers; however, there is no evidence for the presence of long-range transfer involving energy transfer along the chain. Analysis of the data indicates that the rate constant for H atom addition to a phenyl group is approx. 10 times larger than the corresponding rate constant for CH3 radicals. (Author)