Fluorescence Studies of Complex Formation between Hydrophobically Modified Polyelectrolyte and Neutral Polymer in Water

Complex formation between hydrophobically modified (HM) poly(2-(acrylamido)-2-methyl propanesulfonate) (PAMPS) and poly(N-isopropylacrylamide) (PNIPAM) was investigated by nonradiative energy transfer (NRET) and fluorescence quenching techniques by using polymers labeled with naphthalene (Np) and/or pyrene (Py). The results of NRET from Np-labeled HM-PNIPAM to Py-labeled HM-PAMPS indicated that the complex formation occurred between HM-PAMPS and HM-PNIPAM below lower critical solution temperature (LCST) of HM-PNIPAM, and the complex was disrupted above the LCST. By adjusting the ionic strength of the solutions, the critical temperature for the complex formation and disruption could be controlled. Results of the fluorescence quenching of Py-labeled HM-PAMPS in the presence of HM-PNIPAM by Tl+ ions indicated that the comparably stable hydrophobic microdomain was formed due to the formation of the complex.