GAMMA-RADIOLYSIS OF POLY(ACRYLIC ACID) AND POLY(METHACRYLIC ACID)

The COOH group in poly(carboxylic acid)s is especially sensitive to radiation and its degradation can be measured by the formation of CO and CO2. In the gamma-radiolysis of poly(acrylic acid), PAA, and poly(methacrylic acid), PMAA, G(-COOH) has been found to be 8.4 at 77 K and 12.1 at 300 K for PAA, and 6.2 at 77 K and 10.8 at 300 K for PMAA, which are significantly higher than the values for low molecular weight aliphatic carboxylic acids where G(-COOH) is approx. 4-6 in the liquid state and even lower for low molecular weight acids in the solid state. Moreover, the ratio of CO:CO2 is much higher for the polymers (0.35 compared with 0.1). These observations suggest that the degradation proceeds by a somewhat different mechanism in the poly(acid)s. Radical intermediates at 77 and 300 K were identified and their yield measured using electron spin resonance spectroscopy. The mechanism for degradation of carboxylic groups is believed to proceed via both cationic and anionic radicals and we suggest that the pathway through the anion radical may be more important in the polymers and that excited states play a significant role.