Polyolefins in the absence of oxygen

Pure polyolefins contain only C—C and C—H bonds and for that reason the UV absorption spectra should not exceed 200 nm. However, they have extended absorption up to 400 nm (Fig. 3.1) due to the presence of internal and/or external impurities which are also responsible for the fluorescence (Fig. 3.2) and phosphorescence emission (Fig. 3.3) [44, 46, 61, 67-71, 77, 88, 91, 1264]. 

Ultraviolet irradiation of polyolefins in vacuum causes increased absorption (Fig. 3.1), fluorescence (Fig. 3.2) and phosphorescence (Fig. 3.3) absorptions. 

In the absence of oxygen, pure (non-oxidized) polyolefins are relatively stable materials. After long exposure to UV radiation (253.7 nm) in a vacuum or in a nitrogen atmosphere, chain scission, crosslinking and the production of hydrogen, methane and ethane are observed [2058]. 

ESR measurements provide direct evidence for the formation of different types of free radicals (Table 3.2) [331]. 

Polyenyl radicals (3.1), which can be formed in UV irradiated polypropylene according to the reaction  

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