Synthesis and characterization of thermo-insensitive, water-soluble associative polymers with good thickening properties at low and high temperatures

Copolymers composed of acrylamide (AM), N-isopropylacrylamide (NIPAM), and a hydrophobic monomer, either N,N-dihexylacrylamide (DHAM) or N,N-dioctylacrylamide (DOAM), were synthesized using different monomer concentrations by micellar polymerization in aqueous media. Resulting polymers were characterized by molecular weight, final composition, lower critical solution temperature (LCST), and viscoelastic properties on steady-shear state. The effect of the addition of an anionic surfactant, sodium dodecyl sulphate (SDS), was studied in order to increase the viscosity of the solution. Dynamic rheological studies were conducted to achieve a better comprehension of the parameters affecting the viscoelastic behavior of the polymers. This study allows us to understand the relationship between the rheological behavior in aqueous solution with the relaxation time (T_R) and plateau modulus (G₀), taking into account the intra e inter-associations present in the multiblock copolymer (hydrophobic junctions) as well as the interaction between the anionic surfactant with the hydrophobic blocks and with the NIPAM units below and above the LCST of the aqueous system.