Core-shell-corona

Micelles of type (1) were the first investigated examples of ABC triblock copolymer micelles. These micelles are generally characterized by the so-called onion, three-layer, or core-shell-corona structures, i.e., the first insoluble A block forms the micellar core, the second insoluble B block is wrapped around the core, and the third soluble C block extends in the solution to form the micellar corona (Fig. 18). To the best of our knowledge, there are no known examples of ABC block copolymer micelles with A and C insoluble blocks and a B soluble block. 

Core-shell-corona micelles were formed by PEHA-PMMA-PAA triblock copolymers in water, as demonstrated by Kriz et al. [266]. Ishizone et al. [267] synthesized ABC triblock copolymers containing 2-(perfluorobutyl)ethyl methacrylate, tBMA, and 2-(trimethylsilyloxy) ethyl methacrylate with various block sequences. These copolymers were converted into amphiphilic sys-... 

Fig. 18 Schematical representation of different types of micelles formed by ABC triblock copolymers. Core-shell-corona micelles with insoluble core and shell (a), core-shell-corona micelles with radially compartmentalized corona (b), and Janus micelles with laterally compartmentalized corona (c)...

Temperature- and pH-sensitive core-shell-corona micelles were also recently reported by Armes et al. Moreover, the shell of these CSC micelles could be selectively cross-linked [275]. 

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. 

As introduced previously, type 2 ABC triblock copolymer micelles are formed by triblock copolymers containing an insoluble A block while the B and C blocks are soluble in the considered solvent. The insoluble blocks can be located either between the two soluble blocks (BAC structure) or at one end of the triblock (ABC or ACB structures). Micelles of the latter type were discussed above for, e.g., PS-P2VP-PEO pH-responsive micelles and are indeed considered as core-shell-corona, onion, or three-layer structures since the heterogeneity in the micellar corona is observed in the radial direction (Fig. 18). Micelles formed by BAC triblock copolymers are different from the previous case because they can give rise in principle to a heterogenous corona in the lateral dimension (Fig. 18). This could induce the formation of noncentrosymmetric micelles as discussed in Sect. 7.3. 

ABC triblock copolymers have recently proven to be useful in constructing the so-called three-layer, onion, or core-shell-corona micelles, as described in Sect. 7.2. These micelles are characterized by a centrosymmetric structure and a micellar core with two different concentric compartments. Noncentrosymmetric structures from ABC triblock copolymers blended with AC diblocks have, however, been reported in bulk by Goldacker et al. [290]. 

Covalent and metallosupramolecular block copolymers have been combined in a single macromolecular structure. In this respect a terpyridine-functionalized PS-P2 VP has been complexed with a terpyridine-functionalized PEO, leading to a PS32-P2VPi3-[Ru]-PE07o ABC triblock copolymer [330]. This copolymer was further used to prepare core-shell-corona micelles consisting of a PS core, a pH-responsive P2VP shell, and a PEO corona. 

An interesting example of macromolecular co-assemblies derived from starshaped polyionic species was reported by Ge et al. [81]. The authors found that a star-shaped double hydrophilic poly(methacrylic acid)-poly(ethylene oxide) heteroarm copolymer [(PMAA)x-PDVB-(PEO)x, with PDVB being poly(divinylbenzene) and X denoting the number of PMAA and PEG arms] can interact in alkaline media with a double hydrophilic poly(ethylene oxide)-block-quaternized poly[2-(dimethylamino)ethyl methacrylate] (PEO- -PDMAEMAQ) diblock copolymer. At Z = [PDMAEMAQ]/[PMAA] = 1, well-defined water-soluble onion-like (core-shell-corona) macromolecular co-assemblies are formed, with a hydrophobic core consisting of a PDVB microgel. The interaction of the PMA arms of the hybrid coronas of such copolymer stars with the PDMAEMAQ+ blocks of the diblock copolymer generates an insoluble inner layer (shell) around a PDVB core. Meanwhile, PEG blocks from both PEG- -PDMAEMAQ and (PMAA)x-PDVB-(PEG)x build up a hydrophilic nonionic corona that stabilizes the whole complex in aqueous media. 

The results of experimental and theoretical research on water-soluble (nonstoichio-metric) IPECs based on nonlinear (branched) polyionic species (HPE) complexed with oppositely charged linear PEs (GPE) demonstrated that the main feature of such macromolecular co-assemblies is their pronounced compartmentalized structure, which results from a distinctly nonuniform distribution of the linear GPE chains within the intramolecular volume of the branched HPE. In the case of star-shaped PEs or star-like micelles of ionic amphiphilic block copolymers, this com-partmentalization leads to the formation of water-soluble IPECs with core-corona (complex coacervate core) or core-shell-corona (complex coacervate shell) structures, respectively. Water-soluble IPECs based on cylindrical PE brushes appear to exhibit longitudinally undulating structures (necklace) of complex coacervate pearls decorated by the cylindrical PE corona. 

Fig. 4 Representation of the various types of internal organisation that may occur in micelles formed through co-assembly of charged block copolymers. Depicted are micelles with a corona consisting of two different neutral monomers (shown in blue and green) that are (a) mixed, (b) laterally segregated, (c) radially segregated, and (d) laterally and radially segregated. Both cen-trosymmetric micelles (a, c) and non-centrosymmetiic micelles (b, d) are depicted. The micelle with a laterally segregated corona is generally referred to as a Janus micelle (b). The micelle depicted in (c) is most commonly known as onion-like or core-shell-corona micelle. The micelle with a laterally and radially segregated corona (d) is usually called a patched micelle. Note that in the case of (c) and (d) the blue and the red/black chains may also switch position...

Figure 10.1 Various structures of CPBs. (a) Homopolymer brush (b) Core-shell brush (c) Core-shell-corona brush ...

Figure 21 Left AFM height image and cross-sectional analysis of molecular brushes with PnBA-b-PAN-b-PfBA triblock terpolymer side chains. Right Synthetic scheme of template-directed synthesis of carbon nanostructures from core-shell-corona structured PnBA-b-PAN-b-PAA molecular brushes. Reprinted from Tang, C. Dufour, B. Kowalewski, T. Matyjaszewski, K. Macromolecules 2007, 40 (17), 6199-6205, with permission from ACS. ...

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