Effects of salt on the intrinsic viscosity of model alkali-soluble associative polymers

The effects of salt on four model hydrophobically modified alkali-soluble emulsion (HASE) associative polymers were studied. Their reduced viscosities in aqueous solution at different salt concentrations (10(-4) to 10(-1) M) were measured and the corresponding intrinsic viscosities were determined. The results show that the intrinsic viscosity at any given salt concentration decreases as the hydrophobicity of the hydrophobes (i.e., n in the side chain C(n)H(2n+1)) increases. The interpretation is that stronger intra-molecular association of the mon hydrophobic macromonomer leads to smaller polymer molecular coils. An increase of salt content in the solution causes the reduced viscosities of all the model polymers to decrease. This is believed to be the result of excess positive ions in solution which have a shielding effect and reduce the mutual repulsion of the charges along the polymer backbone. In dilute solution the hydrophobic associations of the model associative polymers are predominantly intra-molecular. The addition of salt to the polymer solutions hinders the inter-molecular interaction of the model polymers. The increase in salt content also leads to an increase of intra-molecular aggregations of the hydrophobes of the model associative polymers. Stiffness indices such as the stiffness parameter B and the persistence chain length were used to correlate the polymer conformation of the model associative polymers in NaCl solutions.