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 trimethylammonium group. The macromonomer contents ranged from 0.04 to 0.2 mol%. Associative properties in dilute and semidilute regime were studied by viscosity, static light scattering and rheology measurements. Below the lower critical solution temperature (LCST) the aqueous solution behaviour of the graft copolymers was determined by the balance between intra- and intermolecular side group interactions, which depended on the type of the associative group, the length and degree of grafting of the PEO chains and on external parameters: concentration and temperature. In dilute solution, the polymers containing perfluorooctyl or sulfobetaine groups form aggregates with molar masses depending on the type and the content of the associative group. In semidilute solution, the graft copolymers revealed a shear thinning behaviour. The copolymer with 0.1 mol% PEO chains bearing perfluorooctyl groups showed the greatest viscosity enhancement at low shear rate. Above the phase transition temperature the same copolymer formed an elastic gel.