Fluorescence studies of hydrophobic association of fluorocarbon-modified poly(N-isopropylacrylamide)

A series of hydrophobically associating poly(N-isopropylacryamide) (PNIPAM) containing low amounts (0.06-0.88 mol %) of fluorocarbon (CF3(CF2)(7-)) was prepared by copolymerization of NIPAM and 2-(N-ethylperfluorooctanesulfonamido)ethyl methacrylate. Hydrophobic association of the copolymers in an aqueous medium was investigated by fluorospectroscopy in which both pyrene (By) and fluorocarbon-substituted pyrene (PyCOR(f)) were used as probes. In comparison with unmodified pyrene, using PyCOR(f) with the same fluorocarbon substituent as in the PNIPAM copolymers proved to be more informative for monitoring hydrophobic associations of the copolymers due to its affinity for the microdomains of the fluorocarbon chains. Both the monomer emission intensity, I-375, and the monomer to excimer ratio of intensities, I-375/I-550, Of PyCOR(f) were good indicators of the dependence of the association on the fluorocarbon content of the copolymers and their concentration.