Poly(acrylic acid) with grafted TEMPO moieties, PAA-T, phase separates over the pH range 2-4, whereas at lower and higher pH, the polymer is water-soluble. The pH range of the two-phase region increases linearly with the content of grafted TEMPO moieties. As evidenced by surface tension measurements, the PAA-T molecules have little hydrophobic character. We propose that at low pH PAA-T is an amphoteric polymer that, in addition the anionic carboxyl groups, contains cationic species resulting from the disproportion of TEMPO at low pH. Furthermore, we propose that two-phase regions occur near the isoelectric points of the polymer, suggesting that phase separation is due to electrostatically driven association of polymer molecules.