RADIOLYSIS OF POLY(ACRYLIC ACID) IN AQUEOUS-SOLUTION

Poly(acrylic acid), PAA, reacts with OH-radicals yielding -CH-CH(CO2H)-(beta-radicals) and -CH2-C(CO2H)-(alpha-radicals) in a ratio of approximately 2:1. This estimate is based on pulse radiolysis data where the absorption spectrum of the PAA-radicals was compared with the spectra of alpha-radicals from model systems. The beta-radicals convert slowly into alpha-radicals (k = 0.7 s(-1) at pH 10). This process has also been observed by ESR. At PAA-concentrations of 10(-2) mol dm(-3) chain scission dominates over other competing reactions except at low pH. The rate of chain scission was followed by pulse conductometry and in the pH range 7-9 k = 4 x 10(-2) s(-1) was observed. Oxygen reacts with PAA-radicals with k = 3.1 x 10(8) dm(3) mol(-1) s(-1) at pH 3.5 and k = 1.0 x 10(8) dm(3) mol(-1) s(-1) at pH 10. The corresponding peroxyl radicals undergo slow intramolecular H-transfer yielding a UV-absorbing product whose properties are that of 1,3-diketones.