Poly(acrylic acid) (PAA) was decarboxylated in aqueous solution as a function of pH and ionic strength in the temperature range 100-350 degrees C. Degradation kinetics were first order with respect to acid functionality. The rate of decarboxylation at high pH (E(a) = 51.1 kcal/ mol) was much slower than that at low pH (E(a) = 20.3 kcal/mol). At intermediate pH, the reactivity was found to depend on the degree of dissociation of PAA as a functions of ionic strength, pH, and temperature. No monomer was observed in the reaction product.