Solution behavior and associating structures of a salt-tolerant tetra-polymer containing an allyl-capped macromonomer

Abstract

A novel salt-tolerant macromonomer, allyl-capped octylphenoxy poly(ethylene oxide) (AOP) with the degree of polymerization equal to 20, was synthesized, and then a novel acrylamide(AM)-based tetra-polymer (PSAA) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS), AOP, and vinyl biphenyl (VP) was synthesized by aqueous free-radical copolymerization. Static light scattering measurement shows that the weight-average molecular weight of PSAA is only 6.75 × 10⁶ g/mol, but the z-average radius of gyration in 30 g/L NaCl is up to 189 nm. The apparent viscosities of aqueous PSAA solutions are very low at all polymer concentrations. However, for PSAA in 70 g/L NaCl, the critical association concentration (C _p *) decreases from 0.4 g/L in water to 0.3 g/L, and the apparent viscosity increases sharply with an increase in polymer concentration and is higher surprisingly than that in water above C _p *. The influences of NaCl and CaCl₂ concentrations on solution viscosities of PSAA were measured, and the brine solutions display the strong salt-thickening effect in a wide range of salt concentration. This is different from hydrophobically associating polymers reported in the literature. Moreover, the thickening mechanisms of PSAA in water and brine solutions were investigated by a fluorescent probe and atomic force microscope (AFM).