The structural properties of the polymers poly(methyl methacrylate-co-methacrylic acid) P(MMA-co-MAA), poly(styrene-co-methacrylic acid) P(S-co-MAA), and poly(styrene-co-p-sulfonic acid) P(S-co-SSA) were studied using small-angle X-ray scattering methods. Evidence for ionic aggregation in the dry state and phase separation in the wet state is found for some of the systems. The thin film membrane properties of these polymers as well as poly(styrene-co-acrylic acid) P(S-co-AA) and poIy(vinylcyclohexaneco-acrylic acid) P(VCH-co-AA) were evaluated. The conductivity and the properties of sorbed water were evaluated as a function of increasing ionic content. For each polymer system, an abrupt insulator to conductor transition was found, at water contents which indicate that ionic-aqueous conducting regions in the polymers are randomly distributed whether or not the polymer is phase-separated. The hydrogen bonding of sorbed water in these polymers was studied using near-infrared spectroscopy and compared to that in other hydrophilic polymers.