SynopsisMeasurements were made of dynamic mechanical response spectra and stress-strain properties at room temperature on films of isotactic polypropylene and low-density polyethylene prior and after ultraviolet irradiation in a Xenotest 450 apparatus. The period of irradiation that caused a deep deterioration of ultimate mechanical properties influenced the dynamic mechanical properties only insignificantly. This is attributed to the heterogeneous nature of the photo-oxidative degradation process which is concentrated in a finite number of sites, thus forming crack precursors rather than changing the material properties in bulk. For a biaxially oriented tubular film of low-density polyethylene, anisotropic embrittlement after exposure in Xenotest 450 was observed. This even reversed the order of strain-at-break values in the two main directions of the film. This is remarkably similar to the effect of artificial incisions introduced into the specimens.

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The decomposition of 2,6‐di‐tert‐butyl‐4‐methyl‐4tert‐butylperoxy‐2,5‐cyclohexadienone (I) in n‐heptane solution irradiated with light having wavelengths of 333 nm and 436 nm and in the solid phase irradiated with solar light was investigated. The composition of the reaction mixture was studied by UV and IR spectrometry and chromatographically (gel permeation, thin layer). The radical species was recorded using the electron pulse resonance (EPR) method.

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