Dynamic Light Scattering Characterization of a Water-Soluble Terpolymer with Vinyl Biphenyl in Unsalted and Brine Solutions

Abstract

The sizes and distributions of polymer chains and associating aggregates, hydrophobic associations, and apparent viscosities were investigated with dynamic light scattering (DLS), fluorescence spectroscopy and viscometry for the hydrophobically associating terpolymer poly[acrylamide(AM)/vinyl biphenyl(VP)/sodium 2-acrylamido-2-methylpropane sulphonate(NaAMPS)] (PAAP) in unsalted and brine solutions. The effects of polymer, NaCl concentration, and temperature on the conformation of polymer chains and the formation of associating structures in aqueous solutions were studied. Intra- and inter-molecular hydrophobic associations were formed and the polymer chains were coiled in unsalted solutions below a critical association concentration (Cp*): 0.05 g·dL−1, and the apparent viscosity was very low and varied slightly with polymer concentration, but a large number of large aggregates were formed because of the presence of dominant intermolecular associations above Cp*, and the apparent viscosity increased abruptly with increasing polymer concentration. The PAAP chains were comparatively expanded (Rh: 21–92 nm) in brine solutions, resulted from the simultaneous incorporation of the bulky pendant side groups, including the biphenyl and 2-acrylamido-2-methylpropane sulphonate groups. With the addition of NaCl, large associative aggregates in unsalted solutions were destroyed to form comparatively expanded mono-macromolecules and smaller aggregates. However, as the NaCl concentration was increased from to 15 to 80 g·L−1, more large aggregates were again formed, leading to the obvious salt-thickening behavior. The variation of Rh with temperature proved that intermolecular hydrophobic association is an endothermic process.