Block Copolymers of Styrene and Stearyl Methacrylate. Synthesis and Micellization Properties in Selective Solvents (original) (raw)
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Polystyrene-poly(methacrylic acid) block copolymer micelles
Macromolecules, 1994
Block copolymer micelles formed by diblock and triblock copolymers of styrene and methacrylic acid were characterized in solution in a mixed solvent with 80 vol % of dioxane and 20 vol % of water. Methods of static light scattering, quasielastic light scattering, differential refractometry, viscometry, sedimentation velocity, and densitometry were used. No unattached unimer molecules were observed. Three independent methods were employed for obtaining micellar weights. They agreed well with each other. No anomalous behavior was observed by any method. The micellar solutions were shown to contain almost exclusively single micelles; only a few samples (those producing the largest micelles) contained micellar clusters. The micelles behaved hydrodynamically and thermodynamically as impermeable spheres. The structure of the micellar shell was characterized in some detail. Relations between the aggregation number and the hydrodynamic radius of the micelles on the one hand and the sizes of the styrene and methacrylic acid blocks on the other were presented as scaling type phenomenological equations.
Journal of Liquid Chromatography & Related Technologies, 1999
A size exclusion chromatography study of the micellar system polystyrene-block-poly(methy1 methacrylate) in the mixed solvent 1,4-dioxane/cyclohexane is reported. Good separation of the peaks of micelles enabled direct determination of the weight-average molecular weights of micelles with a low-angle laser light scattering detector. The values obtained were found to be in accordance with those determined independently by static light scattering. Experiments with changing flow rate and concentration of the injected sample solution show moderately fast unimer-micelles reequilibration in the course of the separation. A strong effect of the solute trapping in the column, probably due to the adsorption of the unimer on the packing, was observed.
Journal of Polymer Science Part A: Polymer Chemistry, 2004
The micellization properties of well-defined block copolymers of styrene and decyl methacrylate (SDMA) were studied in two different solvents, methyl acetate (MAc) selective for the polystyrene (PS) block and dodecane, selective for the poly(decyl methacrylate) (PDMA) block. The results were compared with those obtained, in the same solvents, from block copolymers of styrene and stearyl methacrylate (SSMA). In MAc, SDMA copolymers with a decyl methacrylate (DMA) content of 15% or less formed unimolecular micelles, whereas those with a content of 18.5% or higher formed multimolecular micelles. The degrees of association were lower than the corresponding SSMA samples. In dodecane, SDMA form large, monodisperse, spherical, and thermally stable micelles with degrees of association higher than the corresponding SSMA samples. The different behaviors can be attributed to the steric hindrance effect and the ability of the long alkyl groups of the polymethacrylate, MA blocks to crystallize. When the MA blocks are in the soluble corona of the micelles, the steric hindrance effect prevails, thus leading to higher degrees of association for the less bulky alkyl group. In the case where the MA block is in the insoluble core of the micelles, the higher the tendency for crystallization the higher the degree of association.
The Journal of Physical Chemistry B, 2008
Solutions of the polyoxystyrene-polyoxyethylene block copolymer SO 17 EO 65 , where SO denotes polystyrene oxide block as the hydrophobic block and EO the polyethylene oxide block as the hydrophilic block, in mixtures of water (a selective solvent for the EO blocks) and 1,4-dioxane (a good solvent for both blocks) were studied by surface tension and light scattering measurements. Surface and micellar structural parameters have been analyzed as a function of solvent composition. The critical micelle concentration increases and the micellar aggregation number decreases, respectively, as the amount of 1,4-dioxane in the binary solvent increases as a consequence of the enhanced solubility of the SO blocks in the solvent mixture, causing the lowering of the interfacial tension between the hydrophobic blocks in the micellar core and the solvent; therefore, to achieve thermodynamic equilibrium, the micelle size decreases. In addition, static light scattering (SLS) has been proved to be a useful technique to detect the lower boundary of the transition between a dilute micellar solution (sol) to a local-ordered micellar solution (soft gel) resulting from a percolation mechanism. Comparison of the sol-soft gel boundaries obtained from SLS for copolymers SO 17 EO 65 and EO 67 SO 15 EO 67 with those previously derived by rheology is made. Finally, changes in the autocorrelation function of the solutions at the boundary obtained from dynamic light scattering are also analyzed.
European Polymer Journal, 2004
A series of linear triblock terpolymers consisting of polystyrene (PS), polyisoprene (PI) and poly(methyl methacrylate) (PMMA) were examined in tetrahydrofuran (THF), a good solvent for all the blocks and in dimethylacetamide (DMA) and dimethylformamide (DMF), selective solvents for PS and PMMA. In DMA and DMF, which are both non-solvents for PI, multimolecular micelles were formed. The micelles were characterized by low-angle laser light scattering (LALLS), dynamic light scattering (DLS) and viscometry. The aggregation number of the triblock terpolymers was greater in DMF than in DMA, reflecting the higher non-solvent strength of DMF for PI. The aggregation number was also found to increase with increasing PI content of the terpolymers in both DMA and DMF. The hydrodynamic radii depended on the aggregation number of the micelle and the length of the corona forming PS and PMMA blocks. The complexity involved in studying a system consisting of three different polymer blocks is discussed in the context of the results obtained.
Block Copolymer Micelles in Aqueous Media
Collection of Czechoslovak Chemical Communications, 1993
Micellization of di- and triblock copolymers, poly(methacrylic acid)-block-polystyrene and poly(methacrylic acid)-block-polystyrene-block-poly(methacrylic acid), varying in molecular weight and composition, has been studied by static and dynamic light scattering, and sedimentation velocity. Micelles with polystyrene cores were prepared in water-dioxane mixtures, rich in dioxane, and transferred into water-rich mixtures, water, and aqueous buffers via stepwise dialysis. It has been shown that, in dioxane-rich mixtures, the micellar system was in dynamic equilibrium, while in water-rich solvents, water, and aqueous buffers the micellization equilibrium was frozen and micelles behaved like autonomus particles. Under certain conditions, micelles were accompanied by independent large particles. This phenomenon, known from other micellar systems as an "anomalous micellization", is discussed.
Micellar transformations of poly(styrene-b-isoprene) block copolymers in selective solvents
Soft Matter, 2009
The morphology of micelles formed from linear and cyclic poly(styrene-b-isoprene) copolymers (PS 166 -b-PI 278 ) has been studied in solvents with different selectivity for the two block components: heptane and decane, good solvents for the PI block, and DMF, a good solvent for the PS block. Using small and ultra small angle X-ray scattering experiments, SAXS and USAXS, respectively, morphological changes were monitored as a function of the temperature. While micelles formed in DMF were stable and no morphological changes occurred as a function of the temperature, transformations from cylinder-like micelles to vesicles-like objects were observed in both decane and heptane above 60 C for the linear PS-b-PI copolymer. The transition occurred through intermediate steps, where the coexistence between different micellar morphologies was observed. On the contrary, the morphology of the block copolymers with the cyclic architecture was found to be independent of temperature and concentration. For linear blocks, a demicellization was detected at higher temperatures (above 80 C) and the process was fully reversible when the solution was cooled down to ambient temperature. These results are consistent with complementary dynamic light scattering (DLS) observations.
Collection of Czechoslovak Chemical Communications, 2002
The micellization behavior of a hydrophobically modified polystyrene-block-poly(methacrylic acid) diblock copolymer, PS-N-PMA-A, tagged with naphthalene between blocks and with anthracene at the end of the PMA block, was studied in 1,4-dioxane-methanol mixtures by light scattering and fluorescence techniques. The behavior of a single-tagged sample, PS-N-PMA, and low-molar-mass analogues was studied for comparison. Methanol-rich mixtures with 1,4-dioxane are strong selective precipitants for PS. Multimolecular micelles with compact PS cores and PMA shells may be prepared indirectly by dialysis from 1,4-dioxane-rich mixtures, or by a slow titration of copolymer solutions in 1,4-dioxane-rich solvents with methanol under vigorous stirring. In tagged micelles, the naphthalene tag is trapped in nonpolar and fairly viscous core/shell interfacial region. In hydrophobically modified PS-N-PMA-A micelles, the hydrophobic anthracene at the ends of PMA blocks tends to avoid the bulk polar solvent and buries in the shell. The distribution of anthracene tags in the shell is a result of the enthalpy-to-entropy interplay. The measurements of direct nonradiative excitation energy transfer were performed to estimate the distribution of anthracene-tagged PMA ends in the shell. The experimental fluorometric data show that anthracene tags penetrate into the inner shell in methanol-rich solvents. Monte Carlo simulations were performed on model systems to get reference data for analysis of time-resolved fluorescence decay curves. A comparison of experimental and simulated decays indicates that hydrophobic traps return significantly deep into the shell (although not as deep as in + The study is a part of the long-term Research Plan of the School of Science No. MSM 113100001. aqueous media). The combined light scattering, fluorometric and computer simulation study shows that the conformational behavior of shell-forming PMA blocks in non-aqueous media is less affected by the presence of nonpolar traps than that in aqueous media.