Hydrophobically modified poly(sodium 2-acrylamido-2-methylpropanesulfonate)s bearing octadecyl groups: A fluorescence study of their solution properties in water

Fluorescently labeled amphiphilic polyelectrolytes have been prepared by fr ee-radical copolymerization in dimethylformamide using azobis(isobutyronitr ile) as the initiator of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS ) and (1) N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide (PyODA) in 98:2 an d 95:5 molar ratios, (2) N-[2-(1-naphthyl)ethyl]-N-n-octadecylacrylamide (N pODA) in 98:2 and 95:5 molar ratios, and (3) a mixture of the two labeled m onomers in a molar ratio of 95:4:1 (AMPS: NpODA:PyODA). The solution proper ties of the copolymers in water and in salt solutions have been studied by viscometry, H-1 NMR spectroscopy, and fluorescence spectroscopy. Evidence f rom nonradiative energy transfer between excited naphthalene (Np*) and pyre ne (Py) in aqueous solutions of the doubly labeled polymers points to the f ormation of polymeric micelles. The inefficiency of nonradiative energy tra nsfer between Np* and Py in mixed solutions of the singly labeled polymers indicates that the micelles are mostly unimolecular. The quenching of fluor escence of polymer-linked pyrene by nitromethane and thallium nitrate has b een used to assess the accessibility of the chromophore to neutral molecule s and to cationic species, respectively, in water and in solutions of incre asing ionic strength. The results are discussed in light of previous studie s of the properties in solution of neutral polymers carrying the same hydro phobic substituents as PAMPS-Py(Np)ODA and of amphiphilic PAMPS substituted with various other hydrophobic groups.