Reaction Mechanism for Alkyl Radical Formation

The primary event caused by radiation is ionization or direct excitation of polyethylene chains, RH, which leads to the alkyl radical formation. Toriyama et al. [4] proposed a reaction mechanism for the radiation effect on polyethylene based on the ESR study. They presumed that an alkyl radical and an H atom were generated either directly from the dissociation of the excited state polymer or from the recombination between the cation radical and the electron primarily generated by ionization. There are three possible reaction paths involving the charge recombination  

Early in 1961, Libby [30] suggested the proton transfer from the radical cation and subsequent charge recombination between the protonated site of polyethylene chain and an electron for the alkyl radical formation  

This reaction mechanism predicts a small separation distance between the two alkyl radicals in pair determined by the proton-transfer distance. This small separation distance was thought to favor the high yield of the radiation-induced crosslinks. However, the above reaction mechanism seems not to accommodate the results of the ESE study. 

4 Free Radicals in Irradiated Poly(methly methacrylate) 

Among numerous previous studies on the reaction mechanism, Geuskens et al. [31] proposed the most detailed mechanism based on the analysis of radiation products as well as the effect of added ethylmercaptan  

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