The phase behavior of graft copolymers in aqueous solution was investigated. The graft copolymers consist of poly(propylene glycol) (PPG) side chains and N,N-dimethylacrylamide (dMA), N-vinylimidazole (VIm), and N-isopropylacrylamide (iPA), respectively, as backbones. Phase transition temperatures of the PPG copolymers increased with increasing the content of dMA, and iPA as relatively more hydrophilic comonomers and with an increase in the degree of ionization of the incorporated VIm units.