Micellization of polystyrene/poly(2-vinylpyridine) heteroarm star copolymers, PSnPVPn, in aqueous media has been studied by a combination of light scattering and fluorescence techniques. Three copolymer samples differing in numbers of arms and their length form micelles with compact hydrophobic cores and polyelectrolyte poly(2-vinylpyridine) shells. The association number decreases with increasing number of water-soluble arms and their length. Micellization equilibrium is kinetically frozen in aqueous media. The micellar cores are frozen and the behavior of the micellar solutions is controlled by the polyelectrolyte behavior of the polyelectrolyte shell. In the case of the present heteroarm stars with ca. 10 1 arms, the soluble and insoluble arms are strongly segregated and the micellar cores are formed of pure polystyrene as with micelles formed by linear diblock copolymers. As concerns the sample with several tens of arms, a significant steric hindrance, together with a low association number (ca. 4), does not allow for a complete segregation of polystyrene and the poly(2-vinylpyridine) arms. The micellar cores formed by the very hairy star copolymer with several tens of arms contain a fraction of poly(2-vinylpyridine) arms as shown by fluorescence measurements with solubilized pyrene. Alkalimetric titration of an acidic mixture of PSnPVPn micelles with a linear poly(2-vinylpyridine)-block-poly(ethylene oxide) copolymer, PVP-PEO, yields fairly monodisperse spherical onion-skin micelles. The onion-skin micelle has a compact spherical PS core deriving from the parent PSnPVPn micelle, a fairly thin and compact middle layer formed by PVP both from the parent micelle and PVP-PEO copolymer, and a protective PEO shell. The formation of onion-skin micelles is fully reversible and occurs suddenly and very rapidly at pH values higher than 4.8. The "onions" dissociate immediately into PSnPVPn micelles and PVP-PEO copolymer below pH 4.8. Evaluation of the alkalimetric titration data shows that only ca. 40% of the PVP units in the micellar shells are protonized (even in strongly acidic solutions that contain a large surplus of a strong acid, e.g., in 0.1 M HCl). This observation is in agreement with indirect fluorometric data which indicate that in the case of a weak polyelectrolyte, such as poly(2-vinylpyridine), the inner layer of the polyelectrolyte shell close to the core is not ionized.
Formation of polyelectrolyte–surfactant (PE–S) complexes of poly(ethylene oxide)-block-poly(methacrylic acid) (PEO705–PMAA476) and N-dodecylpyridinium chloride (DPCl) in aqueous solution was studied by static and dynamic light scattering (SLS, DLS), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). While it was found previously [Macromolecules 1997, 30, 3519] by microcalorimetric titration that in a similar system (PEO176–PMAA186) crystallization of aliphatic tails of N-dodecylpyridinium bromide did not occur, in our system it was evidenced by SAXS that upon addition of DPCl to fully ionized PEO705–PMAA476 the ordered arrangement of the surfactant occurs in a certain range of PEO705–PMAA476 concentrations and surfactant-to-polyelectrolyte charge molar ratio (Z). Our data suggest a four-step process in the behavior of the PEO705–PMAA476/DPCl system: (i) coexistence of loose aggregates of electrostatically bound surfactants to PMAA block with free and almost unperturbed copolymer coils at Z ≪ 1, (ii) formation of aggregates containing ill-defined cores formed by DPCl micelles attached to coiled PMAA chains (beads-on-a-string nanoparticles) in the range around Z = 0.5, (iii) formation of compact core–shell nanoparticles with a core formed by densely packed ordered (crystalline) DPCl micelles and PEO shell starting slightly before charge equimolarity (Z = 1), and (iv) the region of coexistence of the core–shell nanoparticles with free DPCl micelles in excess above equimolarity (Z ≫ 1). In the region around Z = 0.5, the nanoparticles with nonordered cores coexist in a mixture either with a fraction free chains and large swollen nanoparticles decorated by surfactant micelles (at lower Z) or with the core–shell nanoparticles (at higher Z). PE–S complexes were characterized in detail in terms of molar mass, size, shape, and internal structure.
A new amphiphilic block terpolymer poly((sulfamate-carboxylate)isoprene)-block-polystyrene-block-poly(ethylene oxide), PISC 230 -PS 52 -PEO 151 , with a narrow molecular weight distribution (PDI = 1.05), was synthesized via the post polymerization reaction of the anionically prepared precursor block terpolymer polyisoprene-block-polystyrene-block-poly(ethylene oxide) with chlorosulfonyl isocyanate. The formation and structure of self-assemblies of the polyelectrolyte block terpolymer in dilute aqueous solutions were studied by static and dynamic light scattering, atomic force and cryogenic transmission electron microscopy, fluorometry, and 1 H NMR spectroscopy. In acidic solutions, the terpolymers self-assemble into kinetically trapped multicompartment micelles, with the core consisting of discrete PS and PISC domains and PEO in the shell. If the solution pH is adjusted to the alkaline region, the multicompartment micelles undergo an irreversible transition to regular micelles, with a PS core and a mixed shell formed by PEO and PISC blocks.
The hydration of the poly(oxyethylene) shell in polystyrene-block-poly(2-vinylpyridine)-block-poly(oxyethylene) micelles was investigated by monitoring the solvent relaxation response of a solvent-sensitive fluorophore (patman). It has been found that the relaxation occurs on the nanosecond time scale. Results for triblock copolymer micelles have been compared with those obtained for polystyrene-block-poly(2-vinylpyridine) micelles in order to evaluate the effect of the outer polyoxyethylene layer. Considerable pH-dependent changes in the hydration of poly(oxyethylene) units at the poly(2-vinylpyridine)/polyoxyethylene interface were observed. Additionally, the paper shows that the solvent relaxation technique is a suitable tool for studying polymeric nanoparticles and that the measurement of time-dependent half-width of the emission spectrum allows for estimation of the extent of relaxation process observed by a given experimental setup.
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