The partition of a series of substituted phenols between water and polymer micelles formed
by potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n ranging from 6 to 18, has been
investigated. Steady-state and time-resolved fluorescence measurements have been used to study the
formation and properties of these micelles. The data indicate that just PA-6K2 exhibits a pH-induced
conformational transition. All other copolymers adopt a compact configuration over the entire pH range.
The hydrophobicity of these microdomains, as measured by the ratio III/I, increases with the length of
the side alkyl chain. The aggregation number, i.e., the number of monomer units involved in the
intramolecular micelle, has been found to be equal to the degree of polymerization, suggesting that one
polymer chain forms one polymer micelle. The transfer free energies of p-alkyl-substituted phenols from
water to PA-18K2 and of phenol from water to PA-nK2 have been measured. The contribution of each
methylene group to the free energy is 0.97 and 0.34 kJ mol-1 in the substituted phenol and the side alkyl
chain, respectively. These values are lower than those determined for transfer of phenols to ionic micelles
and to heptane.
Fluorescence spectra of cyclic and linear samples of poly(methylphenylsiloxane) (PMPS) have been measured at 25 °C, in two solvent mixtures (tetrahydrofuran/dioxane and tetrahydrofuran/ methanol), as a function of the solvent composition. The viscosity of the medium ( ) and the segmental density of the macromolecule are varied by changing the solvent composition. The ratio of excimer to monomer intensities (fluorescence ratio, Ie/Im) is independent of segmental density. Ie/Im of linear PMPS is also almost independent on solvent viscosity, but for cyclic PMPS, a direct dependence of Ie/Im on is observed. The analysis of results allows several conclusions: (i) long range excimers are disregarded in the high molecular weight sample; (ii) only less than 10% excimers of any phenylsiloxane, cyclic or linear, are formed in ground-state preformed excimer-forming sites, due to the high dynamic flexibility of siloxanes in the nanosecond time scale; and (iii) excimer dissociation plays a significant role and takes place through a viscosity-dependent mechanism. A model is proposed to explain the viscosity dependence of the fluorescence ratio, which applies both to the high-temperature limit (like the present results of PMPS), and also to some other previously reported results on polymers in the low-temperature limit.
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