The thermoresponsive properties in aqueous solution of the graft copolymer poly(acryhc acid-co-2-acryl-amido-2-methyl propane sulfortic acid)-(delta)-poly(N-isopropylacrylamide) [P(AA-co-AMPSA)-(delta)-PNIPAM] were studied and compared to the corresponding behavior of the poly(acrylic acid)-(delta)-poly(N-isopropylacrylaniide) (PAA-(delta)-PNIPAM) graft product. Both products contain about 40% (w/w) of PNIPAM, whereas the backbone, P(AA-co-AMPSA), of the first copolymer contains about 40% of AMPSA mole units. The strongly charged P(AA-co-AMPSA)-(delta)-PNIPAM graft copolymer was water soluble over the whole pH range, whereas the PAA-(delta)- PNIPAM copolymer precipitated out from water at pH < 4. As a result, the first product exhibited a temperature-sensitive behavior in a wide pH range, extended in the acidic region, whereas in semidilute aqueous solutions, an important thermothickening behavior was observed, even at low pH (pH = 3.0). (C) 2004 Wiley Periodicals, Inc.