A resonance Rayleigh scattering study of unlabeled and pyrene-labeled poly(acrylic acid) polymers

Three different unlabeled poly(acrylic acid) (PAA) polymers, with molecular weight of 2, 150 and 450 kg/mol, and the correspondent PAA labeled with pyrene (PAAMePy polymers) were investigated, in aqueous solution and in dioxane: water mixtures, using the resonance Rayleigh scattering (RRS) technique. The pH showed to strongly affect the polymer conformation and a decrease of the scattering intensity (IRRS) was observed, which is consistent with an increase of the hydrodynamic radius, reflecting an expanded polymer conformation in solution. The obtained pKa values were found higher for the labeled by comparison with the corresponding unlabeled polymers. For the PAAMePy polymers the increment of the water content in dioxane:water mixtures leads to an increase of the IRRS intensity; however, for the unlabeled PAA polymers non-significant differences were observed. In general, for the fluorescently labeled polymers, a good agreement between the present RRS results and those previously obtained from fluorescence measurements could be found.