Time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to study the structure and dynamics of main chain radicals created after 248 nm laser excitation of aqueous solutions of poly(methacrylic acid) (PMAA) and poly(acrylic acid) (PAA). The polymeric radicals are created via Norrish I cleavage of the side-chain carboxyl group. The radicals are characterized by computer simulation of well-resolved, fast motion spectra acquired at high temperature (>100 degrees C). Hyperfine coupling constants and g factors are reported for both PMAA and PAA main-chain radicals. The TREPR signal intensities exhibit a strong dependence on pH, disappearing entirely at pH values >6. Similar to previously studied polymer radicals with ester side chains such as PMMA, symmetry issues play a large role in determining the magnitude of the fast motion coupling constants. Attempts to produce the polymer radicals via a photooxidative mechanism at high pH values failed, and this is discussed in terms of chromophore activity, polymer conformation, and solvent shell effects. The counter radical produced by Norrish I cleavage of the side chain is the hydroxyformyl radical, which is not observed, presumably due to fast spin relaxation. In PAA samples, at least two additional unassigned radicals are observed that may arise from impurities, defect sites, or end-group participation in the photochemistry.