Shell crosslinked polymer micelles

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

The new connective sites provide the opportunity to destroy or disconnect other regions of the nanostructure without destruction of the entire nanoscale entity. This was demonstrated by the excavation of the core of shell crosslinked polymer micelles, by the removal of the colloid from colloidally templated... 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

Huang, H. Remsen, E.E. Wooley, K.L. Amphiphilic core-shell nanospheres obtained by intramicellar shell crosslinking of polymer micelles with poly(ethylene oxide) linkers. Chem. Commun. 1998,13 (13), 1415-1416. 

Two types of poly(2-vinyl pyridine-b-styrene-b-2-vinyl pyridine) triblock copolymers were synthesised by anionic living polymerisation. These polymers formed monodispersed micelles in toluene or toluene/cyclohexane mixture. Poly(2-vinyl pyridine) sequences in the core part of the polymer micelles were crosslinked with 1,4-diiodobutane. After crosslinking, no macrogelation was observed. The morphology of the crosslinked products did not correspond with that of the original triblock copolymer. All products were polystyrene spheres and each of them had one poly(2-vinyl pyridine) core in its centre. It was therefore concluded that the poly(2-vinyl pyridine) core-PS shell type flower microgels were synthesised by crosslinking of the flower micelles in solution. 27 refs. 

Figure 17.8 Schematic of the most commonly reported crosslinking strategies (a-d) utilized in the stabilization of polymer micelles. (Reproduced from E.S. Read and S.R Armes, Recent advances in shell cross-linked micelles, Chemical Communications, 3021-3035,2007, by permission of the Royal Society of Chemistry.)...

Polymer micelle shells can also be stabilised by crosslinking the hydrophilic components. The method was first introdnced by Nystrom and co-workers [53, 54] and Sun and co-workers [55], and has resnlted in more than 80 publications to date. The systems are typically based on amphiphilic block copolymers with a hydrophilic polymer block compromised of polyacrylic acid (PAA). This forms the enter layer of the micelle. These PAA groups can then be crosslinked by amidation with a diamine, and the remaining -COOH groups can be used for further modification with imaging probes, PEG chains or targeting entities, see Figure 2.13. 

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