Grafting of poly(N-isopropylacrylamide) with poly(ethylene oxide) under various reaction conditions

Poly(N-isopropylacrylamides) grafted with varying amounts of poly(ethylene oxide) (PNIPA-g-PEO) were synthesized and studied with differential refract ometry, differential scanning calorimetry, and dynamic light scattering. By free radical reaction between N-isopropylacrylamide (NIPA) and either N-ac ryloylsuccinimide (NASI) or glycidyl methacrylate (GMA), two functional cop olymers, 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 t o the functionalized backbones either in dioxane or in water. Thermal behav ior of PNIPA-g-PEO copolymers in aqueous solutions both below and above LCS T depends on the amount of PEO grafts and on the polymer concentration. Abo ve 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 hydr ophobic interactions, intra- and interchain interactions, and the solubiliz ing effect of PEO on the shrinking backbone.