Functional self-assembling polymeric micelles

The formation of polymeric capsules can also be achieved by the cross-linking of self-assembled amphiphilic block copolymers [85]. The hydrophobic section of the polymer in an aqueous solution will tend to aggregate on the interior of the micelle, whereas the hydrophilic ends will form the outer shell of the micelle. If the hydrophilic end is appropriately functionalized, it can be cross-linked, giving a polymeric shell. The overarching concept is shown in Figure 5.10. 

Polymeric micelles are expected to self-assemble when block copolymers are used for their preparation [28]. Micelles of biocompatible copolymer, viz., PEO with PLA or with PBLA, have been reported in the literature [29,30]. The synthesis of such nanospheres with functional groups on their surface is shown in Fig. 2. 

Similarly, Wasserman and coworkers have studied a wide selection of polymeric materials in aqueous solution that are associative of some kind, i.e., that form some sort of self-assembly through non-covalent interactions [96]. Their study mainly deals with hydrogels of hydrophobically modified polymers, aqueous solutions of polymeric micelles created by block copolymers, and hydrogels based on poly (acrylic acid) and macrodiisocyanates. The spin probes of choice were hydrophobic, such as 5- and 16-DSA (see Eig. 2) or even spin labeled polymers. It was, e.g., possible to screen for the effect of chemical stmcture on the gel formation by recording and understanding the local mobility of the hydrophobic, long chain spin probes as a function of temperature. 

FUNCTIONALIZED POLYMERIC MICELLES BY A SELF-ASSEMBLING OF END-FUNCTIONALIZED PEG BLOCK COPOLYMERS... 

Block-Type Brushes by Sequential Polymerization The sequential hving polymerization of two macromonomers or a macromonomer with a conventional comonomer forms either block-block- or block-coil-type brush structures. For example, giant rod-coil amphiphilic block copolymer bmshes were prepared via a stepwise metallocene-catalyzed polymerization [58]. In the first step, a concentrated solution of methacryloyl end-functionalized PS macromonomer (DP = 18.3, MWD = 1.05) was polymerized by the organosamarium(iii) catalyst in THF. After PS macromonomer was completely consumed, the active center remained living, and tert-butyl methacrylate tert-butyl methacrylate (tBMA) as a comonomer was added to grow the second block. After termination by ethanol, the poly(tert-butyl methacrylate) (PtBMA) coil block was hydrolyzed into a hydrophihc block, poly(methacrylic acid) (PMAA). The final product consisted of a hydrophobic PS brush block and a hydrophihc PMAA coil. The hydrophilic PMAA coil collapsed in nonpolar solvents, which forced the block-coil CPBs to self-assembled into giant micelles with PMAA as the core component and the stiff PS brush block as the shell to stabihze the micelles. 

Using functional molecules as structural directors in the chemical polymerization bath can also produce polyaniline nanostructures. Such structural directors include surfactants [16-18], liquid crystals [19], polyelectrolytes (including DNA) [20,21], or complex bulky dopants [22-24]. It is believed that functional molecules can promote the formation of nanostructured soft condensed phase materials (e.g., micelles and emulsions) that can serve as soft templates for aniline polymerization (Figure 7.3). Polyelectrolytes such as polyacrylic acid, polystyrenesulfonic acid, and DNA can bind aniline monomer molecules, which can be polymerized in situ forming polyaniline nanowires along the polyelectrolyte molecules. Compared to templated syntheses, self-assembly routes are more scalable but they rely on the structural director molecules. It is also difficult to make nanostructures with small diameters (e.g., <50 nm). For example, in the dopant induced self-assembly route, very complex dopants with bulky side groups are needed to obtain nanotubes with diameters smaller than 100 nm, such as sulfonated naphthalene derivatives [23-25], fidlerenes [26], or dendrimers [27,28]. 

Another route to polysilanes that involves the anionic polymerization of dis-ilabicyclooctadienes, which function as sources of masked disilenes (eq. 12), has been described (39,40). Amphiphilic block copolymers formed by this anionic route, such as poly(l,l-dimethyl-2,2-dihexyldisilene)-6-(2-hydroxyethyl methacrylate), undergo self-assembly to form micelles (41). 

One particular asset of structured self-assemblies is their ability to create nano- to microsized domains, snch as cavities, that could be exploited for chemical synthesis and catalysis. Many kinds of organized self-assemblies have been proved to act as efficient nanoreactors, and several chapters of this book discnss some of them such as small discrete supramolecular vessels (Chapter Reactivity In Nanoscale Vessels, Supramolecular Reactivity), dendrimers (Chapter Supramolecular Dendrlmer Chemistry, Soft Matter), or protein cages and virus capsids (Chapter Viruses as Self-Assembled Templates, Self-Processes). In this chapter, we focus on larger and softer self-assembled structures such as micelles, vesicles, liquid crystals (LCs), or gels, which are made of surfactants, block copolymers, or amphiphilic peptides. In addition, only the systems that present a high kinetic lability (i.e., dynamic) of their aggregated building blocks are considered more static objects such as most of polymersomes and molecularly imprinted polymers are discussed elsewhere (Chapters Assembly of Block Copolymers and Molecularly Imprinted Polymers, Soft Matter, respectively). Finally, for each of these dynamic systems, we describe their functional properties with respect to their potential for the promotion and catalysis of molecular and biomolecu-lar transformations, polymerization, self-replication, metal colloid formation, and mineralization processes. 

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