A pH Effect in the HPSEC Separation of Polyacrylamide-Based Copolymers

Four polyacrylamide-based samples, having the same nominal molecular weight and molecular weight distribution, have been characterized by HPSEC using two column sets and a mobile phase of phosphate buffer. Depending upon the pH, the separations demonstrate that the systematic differences between samples are influenced by the level of anionic sites along the polymer chain. It is found that the HPSEC elution profiles of these samples are reversed when the pH is changed from 2.2 to 7.0. The anionicity of the samples ranges from less than 0.5 mole % carboxyl content (the homopolymer of acrylamide) to 33.0 mole %. Capillary viscometry data support these findings in the two solvent media, indicating that no adsorption effects prevail in the chromatography. Static and on-line low angle laser light scattering (LALLS) data on the homopolymer of acrylamide also suggest that no adsorption or degradation is occurring in the chromatographic process.