Polymethylmethacrylate radiolysis

Pulse radiolysis has been seldom used in the detection of intermediates in macromolecular systems. Polystyrene and polymethylmethacrylates in the solid phase have been studied [188—191] while attention has been paid to the solution radiolysis of polyethylene oxide [192]. 

Stepwise decay was also observed when PMMA was irradiated in the presence of ethyl mercaptan (EtSH) [245]. The initial decay rate of the radicals measured at 150°K is proportional to the concentration of EtSH, indicating that the decaying pairs are mixed pairs formed by a radical from PMMA and a radical from EtSH. In fact, radiolysis of pure PMMA results in the formation of pairs of macroradicals. Some are due to main-chain scission, others to hydrogen abstraction from the polymer by CH 3 or CH30 radicals produced by side-chain scission. At 150°K, in pure irradiated polymethylmethacrylate, the mobility of the macroradicals is limited and their rate of decay comparatively low. In the presence of ethyl... 

The nine-line ESR spectrum observed after irradiation at room temperature has been attributed to the propagating radical formed in reaction (7) [76]. However, according to other workers [77] this signal could also result from the addition of another radical to residual monomer molecules. It is of interest to note that the quantum yield of main chain scissions is five to ten times smaller than the quantum yield of side group splitting by reaction (5), whereas both processes occur with the same yield in the radiolysis of polymethylmethacrylate [78]. This indicates that only a fraction of the macro-radicals decompose according to reaction (7) at room temperature. 

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