Monodisperse polystyrenes (M w/M n < 1.15) with molecular weights of 6K, 40K, and 110K and one polydisperse polystyrene (M w/M n = 1.5) with a molecular weight of 110K were synthesized. The chromophore pyrene was randomly and covalently attached onto the polymers. The dynamics of the chains were investigated quantitatively by monitoring the fluorescence of the pyrene monomer. The polymer coil was divided into several blobs among which pyrene is randomly distributed according to a Poisson distribution. The kinetics of the pyrene groups are monitored by only three parameters:  k diff, the rate at which one excited pyrene encounters one ground state (GS) pyrene inside a blob; k e[blob], the product characterizing the exchange of GS pyrene between blobs (k e is the rate of exchange and [blob] is the blob concentration inside the polymer coil); and 〈 n〉, the average number of GS pyrene per blob. We show that the parameters retrieved by this analysis are internally consistent within the theoretical framework of the blob model. A critical polymer chain length is found above which polymer chain dynamics behave in a similar manner, regardless of the size of the polymer. Below the critical polymer chain length, chain dynamics are chain length-dependent.

A hydrophobically modified alkali swellable emulsion copolymer (HASE) was labeled with pyrene and its fluorescence behavior was monitored by steady-state and time-resolved fluorescence as increasing amounts of the surfactant sodium dodecyl sulfate (SDS) were added to the solution. In aqueous solution, the pyrene pendants are aggregated. As SDS is added, the surfactant binds to the pyrene aggregates, which leads to their breakup at an onset SDS concentration of 1.25 x 10(-3) mol/L. The breakup of the pyrene aggregates is complete at 4.25 x 10(-3) mol/L, which is slightly larger than the critical micellar concentration of SDS in 0.01 M Na(2)CO(3) aqueous solution at pH 9 found to equal 3.5 x 10(-3) mol/L by surface tension measurements. The pyrene pendants were present as different species in solution, and the fractions representative of all emissive pyrene species were determined from the global analysis of the monomer and excimer fluorescence decays. Two analyses were applied to the decays. In the first analysis, the diffusional encounters between pyrene pendants were described by the blob model. In the second analysis, no assumptions were made on how the pyrene pendants encountered each other. Both analyses yielded identical results which demonstrate that the determination of the fractions of the different emissive pyrene species of a solution of a pyrene-labeled associative polymer does not depend on the model chosen to account for the diffusional encounters taking place between pyrene pendants.

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A hydrophobically modified alkali swellable emulsion copolymer labeled with pyrene (Py-HASE) was studied by fluorescence, surface tensiometry, and viscometry at concentrations ranging from 0.01 g/L (lower than the overlap concentration, C* = 2.4 g/L) to 10 g/L (above C*) in the presence of the anionic surfactant sodium dodecyl sulfate (SDS). The results obtained by the three techniques lead to the conclusion that binding of SDS onto Py-HASE proceeds in four different stages which are separated by three SDS transition concentrations. The values of the SDS transition concentrations are little affected by the Py-HASE concentration at low Py-HASE concentration but are shifted to higher SDS concentrations at high Py-HASE concentration. The average number of pyrenes per mixed micelle could be determined from the analysis of the fluorescence decays which established a maximum average capacity of pyrenes per mixed micelle of 2.4 ± 0.5 independent of the polymer concentration. For a Py-HASE concentration of 6.0 g/L, the average number of pyrenes per mixed micelle was found to take the optimal value of 2.0 at the SDS concentration where the solution viscosity peaked. This study constitutes the first example where fluorescence experiments are being used to rationalize the spike in viscosity exhibited by an associative thickener solution upon addition of a surfactant.

The molar absorption coefficient of pyrene aggregates, epsilon(E0), was determined for a series of pyrene-labeled poly(N,N-dimethylacrylamide)s (Py-PDMA) having different pyrene contents. Aqueous solutions of Py-PDMA having pyrene contents ranging from 263 to 645 mumol of pyrene per gram of polymer were studied by UV-vis absorbance and time-resolved fluorescence spectroscopy. The global analysis of the monomer and excimer fluorescence decays with the fluorescence blob model yielded the fractions of the overall absorption contributed by all the pyrene species present in solution. The combined knowledge of the fractions obtained from the global analysis of the time-resolved fluorescence decays, the total absorption of the Py-PDMA solution obtained from UV-vis spectroscopy, and the total pyrene concentration in the solution obtained from the known pyrene content of each Py-PDMA sample led to the determination of the molar absorption coefficient of pyrene aggregates. Regardless of the pyrene content of the Py-PDMA samples and hence the level of association of the pyrene pendants in solution, all Py-PDMA samples yielded similar epsilon(E0) values over the range of wavelengths studied, namely, from 325 to 350 nm. The averaged epsilon(E0) was found to be red-shifted relative to unassociated pyrenes by 3 nm as well as having a value at the 0-0 peak of 21 000 M(-1).cm(-1) reduced from 34 700 M(-1).cm(-1) for unassociated pyrenes. The determination of epsilon(E0) enabled the first determination of the absolute fraction of associated pyrenes for aqueous solutions of a series of pyrene-labeled water-soluble polymers. The procedure outlined in this study is applicable to any pyrene-labeled water-soluble polymer and provides a new means to study quantitatively the effect of the hydrophilic-to-lipophilic balance on the hydrophobic associations generated by hydrophobically modified water-soluble polymers. As an application, the average number of pyrenes involved in a pyrene aggregate generated by Py-PDMA in water is determined.