Synthesis and spectroscopic characterization of fluorescently labeled hydrocarbon- and/or fluorocarbon-modified poly(sodium 2-acrylamido-2-methylpropanesulfonates)

Fluorescently labeled amphiphilic polyelectrolytes bearing naphthalene (Np) or pyrene (Py) chromophores, hydrocarbon and/or fluorocarbon chains have been prepared by free-radical polymerization using azobis(isobutyronitrile) (AIBN) as an initiator in N,N-dimethylformamide (DMF). The five different Py labeled polymers prepared are (i) a copolymer of sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) and N-n-dodecyl-N-[4-(1-pyrenyl)butyl]acrylamide (PyDodAm) in a molar ratio of 95:5, (ii) two terpolymers of NaAMPS, PyDodAm, and N-n-dodecylacrylamide (DodAm) in 90:5:5 and 80:5:15 molar ratios, and (iii) two terpolymers of NaAMPS, N-n-1H,1H-perfluorooctyl-N-[4-(1-pyrenyl)butyl]acrylamide (PyOctAm), and N-n-1H,1H-perfluorooctylacrylamide (OctAm) or DodAm in a molar ratio of 80:5:15. The four different Np labeled polymers are terpolymers of NaAMPS, N-n-dodecyl-N-[2-(1-naphthyl)ethyl]acrylamide (NpDodAm) or N-n-1H,1H-perfluorooctyl-N-[2-(1-naphthyl)ethyl]acrylamide (NpOctAm), and DodAm or OctAm in a molar ratio of 80:5:15. The polymers were characterized by FTIR, 1H and 19F NMR, and fluorescence spectroscopy. Their solution properties in water and in NaCl solutions have been studied by surface tension and dynamic light scattering measurements. Fluorescence depolarization determinations indicate that local motions of Np are more restricted in the hydrophobic nanodomains formed by fluorocarbon chains than in those formed by hydrocarbon chains. Experiments based on the non-radiative energy transfer from excited Np (Np*) to Py in mixed solutions of the singly labeled polymers, which bear either Np or Py chromophores, reveal the absence of interpolymeric micelles. All polymers exhibit a low activity on the air/water interface even for solutions of polymer concentrations up to 10 g L−1 (∼55 mN m−1). In aqueous solutions, the polymers form polymeric micellar structures with an average diameter of ∼20 nm (20 °C, 1 g L−1).