Poly(acrylic acid) has a pKa around 4.2: it implies it would be in its completely undissociated form in strongly acid media. That would make macromolecular dimensions to decrease, as there would be no repulsion between carboxylate groups.
On the other hand, the presence of undissociated COOH groups will favor the occurrence of intra- and intermolecular hydrogen bonding. Depending on macromolecular weight, this may result in formation of insoluble clusters.