Two polyethylene glycols (PEG, M = 35 000) end-capped with short fluorocarbon tails were synthesized and characterized. In aqueous solution, the fluorocarbon portions associate strongly to form micelle-like structures which are bridged by PEG chains to form a three-dimensional network. As a result, these polymers in solution exhibit unusual rheological properties as a function of fluorocarbon length, polymer concentration, and shear rate (frequency). Their zero-shear viscosity increases with concentration, a common behavior of associating polymers. The viscosity is dramatically enhanced by replacing the end hydrophobe C6F13 with C8F17, a consequence of the stronger association interaction of C8F17 in aqueous solution. The polymer with the longer end group exhibits strong shear thinning once a critical shear rate is reached, whereas for the C6F13 end-capped polymer, we cannot with our equipment reach the shear-thinning regime. Our data indicate that between 2 and 6 wt %, and perhaps over a wider range of concentrations, both systems can be characterized in terms of identical values of the plateau modulus G N°, implying a similar concentration of chains bridging micelles in each system. The G N° values increase strongly with polymer concentration, consistent with a larger fraction of bridging chains and a smaller fraction of looping chains at elevated concentration. The viscosity difference between the two polymers can be explained in terms of a slower exit rate of the longer fluorocarbon from its micelle.

The syntheses of three novel functionalized tricarbocyanine dyes are described. These dyes containing isothiocyanate and succinimidyl ester functional groups are reactive toward primary amines and can be used as fluorescent probes for biologically pertinent compounds such as amino acids and functionalized dideoxynucleotides. The absorption and fluorescence maxima occur in the near-IR region of the spectrum (770-810 nm). The succinimidyl ester proved to be very sensitive to hydrolysis and was generated in situ to label amino acids. The isothiocyanates were less susceptible to hydrolysis and were conjugated using organic modified [40% (v/v) acetonitrile] buffers to amino acids. A dye with an alkyl isothiocyanate moiety showed conjugation to amino-functionalized dideoxynucleotide triphosphates.

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19F NMR experiments are used to study the aggregation behavior of two telechelic polymer systems. These polymer systems consist of a water−soluble chain, here poly(ethylene glycol), with two hydrophobic endgroups. Because of the hydrophobic interaction of the fluorocarbon endgroups, these polymer chains associate in water to form aggregates at low concentrations. The aggregate comprises a core formed from the insoluble hydrophobic endgroups that are surrounded by a corona of long water-soluble polymer chains. With increasing polymer concentration, the polymer chains start bridging so that a three-dimensional, physical network with fluorinated aggregate cores as cross-link points is formed. This effect can be substantially enhanced by replacing the hydrophobic endgroup C6F13 with C8F17, a consequence of the stronger association of C8F17 in aqueous solution. By different 19F NMR parameters, i.e., 19F transverse relaxation and 19F chemical shift, we can distinguish aggregated and nonaggregated chain ends. This enables us to follow the formation of an infinite network.