PS-PMA micelle

We addressed the above problem by studying a system of modified PS-PMA micelles with long PMA blocks end-tagged by a strongly hydrophobic molecule in mixtures of water with organic solvents and in purely aqueous media where electrostatic effects dominate the behavior [93-96]. We used anthracene (An) as the end-attached hydrophobic group, which allowed for fluorescence study. When we started the study, it was not a priori clear what would happen when such slightly modified micelles were dispersed in aqueous media. 

Fig. 15 Experimental kinetic NRET curves (Np-to-An energy transfer) of fluorescently labeled PS-PMA micelles in 5% water, 95% 1,4-dioxane top) in 20% water, 80% 1,4-dioxane center)-, and in water bottom). Experimental data fitted by multiexponential functions...

Fig. 16 Hydrophobically modified PS-PMA micelles with attached Np and An probes...

Fig. 27 Simulated concentration profile (black circles correspond to left axis) and electrostatic potential (white circles correspond to right axis) in PS-PMA micelles as a function of the distance from the micellar center for pH 5 and ionic strength 0.001...

Fig. 28 Simulated distributions of radial distances of end segments from the core in hydrophobi-cally modified black circles) and unmodified white circles) PS-PMA micelles...

Fig. 29 Comparison of experimental curve (noisy) and simulated data (circles) describing the NRET kinetics of fluorescently labeled PS-PMA micelles...

For some applications, it is desirable to lock the micellar structure by cross-Hnking one of the micellar compartments, as discussed previously in Sect. 2.6. Cross-Hnked core-shell-corona micelles have been prepared and investigated by several groups as illustrated by the work of Wooley and Ma [278], who reported the cross-linking of PS-PMA-PAA micelles in aqueous solution by amidation of the PAA shell. Very recently, Wooley et al. prepared toroidal block copolymer micelles from similar PS-PMA-PAA copolymers dissolved in a mixture of water, THF, and 2,2-(ethylenedioxy)diethylamine [279]. Under optimized conditions, the toroidal phase was the predominant structure of the amphiphilic triblock copolymer (Fig. 19). The collapse of the negatively charged cylindrical micelles into toroids was found to be driven by the divalent 2,2-(ethylenedioxy)diethylamine cation. 

Micellization of PS-PMA diblock and triblock copolymers in 80 20 dioxane water mixtures was investigated by Qin et al. (1994) using static and quasi-elastic light scattering, differential refractometry, viscomelry, sedimentation... 

Block copolymers of polystyrene (PS) and poly(methacrylic acid) (PMA) form spherical micelles in water, with a glassy core of PS blocks and extended PMA block chains forming a corona [16-18]. However, the PS-PMA block copolymers cannot be dissolved directly into water. In a dioxane-water (80 20, v/v) mixture, the PS-PMA block copolymers undergo closed association to form equilibrium micelles. A stepwise dialysis of the dioxane-water solution of the PS-PMA block copolymers, with a gradual increase in water content, eventually allows one to obtain an optically clear aqueous solution of micelles, which are referred to as kinetically frozen micelles [18]. 

Fig. 19 TEM image of toroidal micelles from a PAA-PMA-PS triblock copolymer (A). This sample was cast from a solution with 0.1 wt% PAA99-PMA73-PS66 triblock copolymer, a THF water volume ratio of 1 2, and an amine acid molar ratio of 0.5 1 by addition of 2,2-(ethylenedioxy)diethylamine. The cast film was negatively stained with uranyl acetate. A schematical representation of theses micelles is also shown (B). Reprinted with permission from [279], Copyright (2004) American Association for the Advancement of Science...

Figure 9 Top cartoon representations of a spherical micelle, a wormlike micelle, and a vesicle. The red blocks represent the solvophilic blocks, and the blue blocks represent the solvophobic blocks. Bottom example TEM images showing diffa-ent micelle morphologies adopted by block copolymers in solution, (a) Spherical micelles formed from polyfethylene oxide)-f>-polycaprolactone (PEO-f>-PCL) copolymers.(b) Wormlike micelles, vesicles, and octupi formed by mixing PEO-fc-polybutadiene (PEO-fc-PB) block copolymers. (Reproduced from Ref. 32. American Chemical Society, 2004.) (c) Vesicles formed from PEO-f>-PCL copolymers. (Reproduced from Ref. 33. Royal Society of Chemistry, 2011.) (d) Multicompartment micelles formed from a triblock copolyma-. (Reproduced from Ref. 34. American Chemical Society, 2010.) (e) Stomatocytes formed using PEO-f>-polystyrene (PEO-f>-PS) copolyma-s. (Reproduced from Ref. 35. American Chemical Society, 2010.) (f) Toroidal micelles coexisting with cylindrical micelles and sphaical micelles formed from poly(acrylic acid)-f>-poly(methacrylic acid)-fc-PS (PAA-f>-PMA-f>-PS) triblock copolymers. (Reproduced from Ref. 36. Royal Society of Chemistry, 2009.)...

PS-co-PAA)-b-PAA and PS-b-(PAA-co-PMA) block copolymers, with one sequence being a random copolymer, were recently examined by LarueUe et cd. [184] and by Zhang et al. [185] in order to tailor the hydrophilic/hydrophobic characteristics of the micellar core or shell. Poly(perfluoromethacrylate)-PAA block copolymer micelles, studied by Ito et al. [186] represent in this respect an extreme case of solubility difference between core and shell. 

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