Amphiphilic copolymers with thermosensitive and pH-sensitive properties were prepared by grafting methoxy poly(ethylene glycol) (MPEG) of different molecular weights onto alternating copolymers of maleic anhydride with styrene and 4-tert-butylstyrene. Aqueous solutions of these graft copolymers exhibit lower critical solution temperatures (LCST). These LCST's are highly sensitive to changes in pH and salinity and to the presence of hydrophobic and hydrogen-bonding additives. The phase transitions are attributed to the cooperative effects of both hydrophobic interactions and intra/ intermolecular hydrogen-bonding interactions.