Associative graft copolymers comprising a poly(N-isopropylacrylamide) backbone and end-functionalized polyoxyethylene side chains. Synthesis and aqueous solution properties

Novel, water-soluble associative graft copolymers were prepared by radical copolymerization of N-isopropylacrylamide (NIPAAm) and polyoxyethylene (PEO ) macromonomer bearing a terminal perfluorooctyl, sulfobetaine or trimethyl ammonium group. The macromonomer contents ranged from 0.04 to 0.2 mol%. Ass ociative properties in dilute and semidilute regime were studied by viscosi ty, static light scattering and rheology measurements. Below the lower crit ical solution temperature (LCST) the aqueous solution behaviour of the graf t copolymers was determined by the balance between intra- and intermolecula r side group interactions, which depended on the type of the associative gr oup, the length and degree of grafting of the PEO chains and on external pa rameters: concentration and temperature. In dilute solution, the polymers c ontaining perfluorooctyl or sulfobetaine groups form aggregates with molar masses depending on the type and the content of the associative group. In s emidilute solution, the graft copolymers revealed a shear thinning behaviou r. The copolymer with 0.1 mol% PEO chains bearing perfluorooctyl groups sho wed the greatest viscosity enhancement at low shear rate. Above the phase t ransition temperature the same copolymer formed an elastic gel. (C) 2001 El sevier Science Ltd. All rights reserved.