ESR Studies on Pyrolyzed and Irradiated Polyacrylonitrile

ESR studies are carried out at temperatures from 77 to -196°C for polyacrylonitrile (PAN) pyrolyzed in the temperature up to 700°C and for the one irradiated with ultraviolet light and γ-ray. The ESR spectra for PAN pyrolyzed below 600°C are considered to be due to a free radical because they are independent of the measurement temperature. The g -values are found to decrease with increasing pyrolysis temperature and a possible explanation is proposed. The ESR spectra for PAN pyrolyzed above 650°C are sensitively affected by being exposed to air and change with the measurement temperature in a complicated way; the broad and narrow lines are observed and it may be speculated that the former and latter are, respectively, due to a conduction electron and a free radical. For PAN irradiated with ultraviolet light and the one with γ-ray, hyperfine structure (hfs) is observed in the ESR spectra in contrast with those for pyrolyzed PAN. The hfs lines are well explained by two types of free radical likely to be produced.