ESR and the Mechanism of Radiolysis

The number of different types of radicals observed in the ESR spectra of irradiated polymers is always greater after irradiation at 77 K than at 300 K. The 

Figwe 10.12 ESR spectra of polystyrene after y-irradiation in vacuum. Radiation dose 100kGy, radiation temperature (a) 77K, (b) 300K 

Flgpie 10.13 ESR spectra of random copolymers of styrene and methyl methacrylate after y rradiation in vacuum at 300K. Radiation dose SlcGy. The compositions of the copolymers are specified in mol% styrene 

FIpBc I61I4 Protective effect against degradation by y radiation provided by styrene units in random copolymers of styrene and methyl methacrylate, shown by tim radical yidds G(R ) derived from the ESR spectra, (a) Experimental values for y irradiation at 77 K (b) experimental values for r in ation at 300 K. The lines correspond to the G(R ) values for the copolymers calculated from the G(R ) values for poly(mediyl methacrylate) and polystyreiK based on the additivity of electron densities 

ESR provides a powerful technique for developing a fundamental understanding of the mechanism and kinetics of free radical polymerization and of the mechanism of degradation of polymers by high-energy radiation. The assignment of ESR spectra to component radicals and the measurement of the concentrations of these radicals require a variety of experimental and computational procedures, which have been greatly enhanced by improvements in spectrometer performance and computer capabilities. 

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