Polyelectrolytes microdomains

Micellar media created by sodium dodecyl sulfate or cetyltrimethylammon-ium bromide have also a positive effect on the ortho selectivity [262,269-271]. In a recent article, the PFR of 1-naphthyl acetate in aqueous solutions of an antenna polyelectrolyte like poly(sodium styrenesulfonate-co-2-vinylfluorene) has been reported, which, in addition to the micellar effect, also provides singlet sensitization by means of fluorene chromophores. In this particular case, the occurrence of in-cage versus out-of-cage processes can be clearly correlated with the different packing of the microdomains, which depends on the molar fraction of monomers in the antenna copolymer [272]. 

Khokhlov, A.R., Nyrkova, I.A. (1992). Compatibility enhancement and microdomain structuring in weakly charged polyelectrolyte mixtures. Macromolecules, 25, 1493-1502. 

Y. Morishima, M. Tsuji, M. Kamachi, and K. Hatada, Photochromic isomerization of azobenzene moieties compartmentalized in hydrophobic microdomains in a microphase structure of amphiphilic polyelectrolytes, Macromolecules 25, 4406-4410 (1992). 

Synthetic weak polyelectrolytes provide hydrophobic microdomains in the low pH range. Typical examples are poly(methacrylic acid) (PMA) (i-3), copolymers of maleic anhydride and n-alkylvinyl ethers (n = 4-9) 4, 5), and copolymers of maleic anhydride and styrene or methylstyrene (6). The compact polymer coils are formed only in acidic solution, but the compact conformation is converted into the extended rod or coil form at high pH because of repulsion of ionized carboxyl groups. At low pH, many hydrophobic molecules can be hosted by the polymer coils, a condition that disappears at high pH. However, a hydrophobic environment is required... 

These data indicate that the environment of CnPN in PMA and in PA-I8K2, both at pH 8, where both polyelectrolytes are almost fully ionized, is quite different. C PN experiences a water phase in PMA, and the interaction between CnPN and PMA is electrostatic in nature. In PA-I8K2 solution, CijPN was solubilized in polymer hydrophobic microdomains because of a hydrophobic interaction between the long hydrocarbon chains and because of electrostatic bonding. 

Synthetic polyelectrolytes containing hydrophobic microdomains provide a challenging subject for investigation not only for their own intrinsic... 

Finally, we wish to emphasize that a general picture of the conformational state of a polyelectrolyte is connected to the experimental method used in order to elucidate it. Regarding this, poten-tiometric and viscometric data may led us to ascertain the overall conformational state of the macromolecular chains, whereas dye binding studies (equilibrium dialysis, absorption spectroscopy, fluorescence, optical activity) are much more sensitive to local conformational states. In our opinion, these latter methods can be conveniently employed in ascertaining hydrophobic microdomains. 

Physico-chemical properties of the microdomain of polymer complexes have been studied by means of Ih-NMR I, light scattering , or fluorescence polarization. Here, the authors tried to evtiluate the microdomain of polymer complexes by the electrochemical cissay. The formation of polyion complex affected the redox behavior of poly-(viologen)s considerably. Fig. 1 shows the cyclic voltammograms for PXV-PSS complex coated electrode. The first redox peak shifted to positive side, and peak broadening was observed by the complex formation. It is clear that the redox behavior was restricted by the complexation. It is known that the electron transfer process must accompany the migration of counter ions to maintain electroneutrality. As in polymer complex microdomain, polyelectrolyte chains interacted with each other and decreased their free volume, they should thereby provide the domain with smaller porosity. 

Jones, G., II and Oh, C., Photophysical and electron-transfer properties of pseudoisocyanine in the hydrophobic microdomain of an aqueous polyelectrolyte, /. Phys. Chem., 98,2367,1994. Lui, M., Kira, A., and Nakahara, H., Two-dimentional aggregation of a long-chain thiacarbocyanine dye monolayer on polyanion subphases, /. Phys. Chem., 100, 20138, 1996. 

The cac concept is less useful when considering the association between hydrophobicaUy modified (HM) polyelectrolytes and surfactants. The reason is that the HM polyelectrolytes themselves associate and form hydrophobic microdomains into which added surfactants can be incorporated [30], a process akin to mixed micelle formation [31]. Hence, even at low concentrations the surfactants added to the polymer solution can be incorporated in the hydrophobic microdomains present. A consequence of this is that pol5uner-surfactant complexation occurs over a broader range of surfactant concentration and it is difficult to determine a critical concentration. 

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