Photodegradation of polyacrylonitrile in solution

Abstract

The ultraviolet photodegradation of polyacrylonitrile was studied at 25°C. with irradiation with light of wavelength 2537 A. Polymer dissolved in a 80%/20% mixture by weight of ethylene carbonate and propylene carbonate was irradiated. Preliminary experiments indicated that in the presence of oxygen predominantly chain scission takes place, whereas in its absence chain scission and recombination of radicals seem to occur. There is also a dark reaction which proceeds for appreciable periods of time after exposure. Quantitative studies were performed in vacuo at 25°C. in the ethylene carbonate–propylene carbonate mixture as solvent. Degradation was followed by determining intrinsic viscosities as a function of time at various light intensities. The quantum yield was found to be 7.7 × 10−4 chain scissions for each quantum absorbed under the given experimental conditions. Infrared spectra of original and irradiated polymer samples indicate that there is no change in the overall structure of the polymer chains. The experimental results can be satisfactorily represented by the theory of random breaking of bonds assuming that the rate of breaking bonds is proportional to the number of bonds present at any time t and to the light intensity. The experimental rate constants derived on the basis of the random theory were actually found to be linearly dependent on the light intensity.