Electron spin resonance studies of irradiated polypropylene

Polypropylene has been irradiated at −196°C. and its electron spin resonance spectra studied at temperatures between −196°C. and room temperature. The intensity of the eight‐line spectrum observed at −196°C. corresponded to a G for radical production of 3.3. The spectrum could be reconstructed from theoretical curves assuming equal concentrations of radicals with four‐ and eight‐line spectra. On warming to room temperature the radical concentration was reduced to 30% of the initial concentration. In experiments in which the sample was warmed to −100°C. no change in radical concentration was observed. Annealing experiments at temperatures between −100°C. and the glass transition temperature showed that at each temperature there was a rapid decay of radicals after which no further change in radical concentration took place. Above the glass transition temperature a continuous decay occurred. The onset of decay above −100°C. may be associated with the onset of segmental motion in the amorphous regions of the polymer. The rapid decay of the radicals suggests that they are formed near each other as the results of hot hydrogen atom reactions.