Comparison of the ultraviolet and γ‐ray induced production of unsaturation and color in polyvinyl chloride

A study was made of the spectroscopic changes produced in thin polyvinyl chloride films when irradiated in vacuum at room temperature with UV, and γ‐radiation. At doses up to 2·1022 quanta/g. PVC of UV radiation (2200–3400 Å.), or 100 Mrad of γ‐rays, the kinetic plots for increased absorbance throughout the UV‐visible spectrum brought about by these two radiations are fully superimposable. In terms of absorbed energy units needed to produce the same spectroscopic changes (and hence the same conjugated unsaturation or the same HCl evolution), it was thus found that γ‐radiation is about 13 times as efficient as UV radiation. This result, for films containing some 3 to 5% residual ketonic solvent, correlates very well with corresponding literature data on the photo‐ and radiation chemical evolution of HCl from solvent‐free PVC. The quantum yield for the former process is shown to be independent of wavelength below 3400 Å., which is the effective photochemical cut‐off wavelength. The area under the UV‐visible spectrum, as well as the solar absorptivity, reaches a maximum value after a UV dose of about 1 to 2·1023 quanta/g.