AbstractInfrared spectroscopy studies were undertaken to determine the effects of ultraviolet light radiation on a methylsiloxane resin. The results indicate that SiCH2Si linkages were formed as a result of irradiation at wavelengths above 281 mμ from a xenon are lamp; on the other hand, SiOH and SiCH2CH2Si linkages were formed instead when the resin was exposed to the lower wavelengths emitted from a mercury vapor lamp. The different effects on the resin induced by the two ultraviolet light sources are attributed to the fact that only the energies from the mercury vapor lamp radiation are sufficient to cause the excitation of oxygen molecules in the air surrounding the irradiated polymer. The excited oxygen molecules prevented the formation of SiCH2Si structures by interacting with active %tbond;Si units that were formed as a result of SiC bond rupture to produce SiOH; SiCH2CH2Si linkages were formed as the result of a secondary reaction.