Poly(N-isopropylacrylamides) grafted with varying amounts of poly(ethylene oxide) (PNIPA-g-PEO) were synthesized and studied with differential refractometry, differential scanning calorimetry, and dynamic light scattering. By free radical reaction between N-isopropylacrylamide (NIPA) and either N-acryloylsuccinimide (NASI) or glycidyl methacrylate (GMA), two functional copolymers, PNIPA-co-NASI (M-w = 1.9 x 10(5)) and PNIPA-co-GMA (M-w = 1.8 x 10(5)), were synthesized. Various amounts of PEO (M-w = 6000) were attached to the functionalized backbones either in dioxane or in water. Thermal behavior of PNIPA-g-PEO copolymers in aqueous solutions both below and above LCST depends on the amount of PEO grafts and on the polymer concentration. Above the LCST, the size of the aggregates of the graft copolymers sterically stabilized by a low number of PEO grafts is dependent on these two factors. Factors determining the shrinking and collapse of PNIPA-g-PEO include hydrophobic interactions, intra- and interchain interactions, and the solubilizing effect of PEO on the shrinking backbone.