New approach to the molecular characterization of hydrophobically modified polyacrylamide

A new approach to the molecular characterization of hydrophobically associating copolymers of acrylamide is developed. It is based on the study of associative properties: the formation of intermolecular aggregates was followed by dynamic and static light scattering (DLS and SLS), while the formation of hydrophobic domains was detected by fluorescence spectroscopy with pyrene as a probe. In aqueous media, hydrophobic aggregation begins at concentrations much lower than the overlap concentration. The addition of co-solvent, acetonitrile, shifts the aggregation to the semi-dilute region. The dissolution of hydrophobic aggregates is controlled both by fluorescence spectroscopy with pyrene as a probe and by DLS and SLS. Absolute Mw values are measured by SLS in mixed solvent of optimal composition. Molecular weight distribution (MWD) is characterized by GPC using calibration with secondary standards characterized by SLS. This approach allowed us to follow MWD evolution during a micellar copolymerization of acrylamide, N-nonylacrylamide and acrylic acid. It is found that the molecular weight heterogeneity remarkably growths with the increase of conversion.