Block self-assembly

If supramolecular bundles are formed spontaneously in bulk films, by inclusion of appropriate reactive groups it should be possible to convert these into molecular objects by cross-linking, while maintaining the precise size and shape of the rod bundles. A coil-rod-coil triblock molecule 22 based on linear PPO (fcon = 0.73) with a reactive rod block self-assembles into discrete rod bundles that are encapsulated by PPO coils and subsequently organize... 

In contrast to self-assembly or self-organization, which rely on the intrinsic properties of a system, template-assisted assembly provides a way to externally control the formation of a structure. The template contains spatial information, which is expUcitly imposed on the building blocks of a system. In a first step this can be a mild template effect, which only assists in the pattern formation. This effect is encountered, for example, in the structure formation of PTCDA on Ag(l 11) and Ag(l 10) [8]. In these cases the final structure of the overlayer is not only controlled by the mutual interaction of the PTCDA building blocks (self-assembly) but also assisted by the substrate. The different crystallographic orientation of the respective surfaces leads to the formation of either a herringbone pattern or a Hnear assembly on Ag(l 11) and Ag(l 10), respectively (Fig. 2). Similar results have been found for PTCDA on Cu(l 11) [9] and Cu(l 10) [10] as well as Au(l 11) and Au(lOO) [llj. 

One year before, Stoddart et al. described the diastereo-selective self-assembly of [2]catenanes (Scheme 8). Catenanes incorporating complementary jt-electron-rich and Tt-electron-deficient macrocyclic components with binaphthol building blocks self-assemble from appropriate precursors. If one of the components is present as a racemate and the other as an enantiopure compoxmd, the formation of two diastereoisomers is possible. The dia-stereoselective self-assembly into [2]catenanes occurs through the formation of intermediate diastereoisomeric complexes. In a subsequent step, the open ring is again cyclized and the catenane formed with a diastereomeric excess of 33%. 

Pyrolysis of PFS polymers yields nanocomposites containing magnetic Fe clusters with tunable magnetic properties [16]. Finally, block copolymers containing PFS blocks self-assemble, generating remarkable nanoarchitectures such as cylindrical micelles in selective solvents [17,18]. Con-... 

Not only small molecular facial amphiphiles have been described but also polymeric facial amphiphiles. Amphiphilicity can be induced in polymers by using hydrophilic and hydrophobic blocks. Self-assembly of such head-tail amphiphilic block copolymers has extensively been described and is controlled by phase separation of the hydrophilic and hydrophobic blocks and their volume fractions. On the contrary, facial amphiphilic polymers can be obtained from alternating copolymers of hydrophilic and hydrophobic monomers, or by polymerization of facial amphiphilic monomers. 

A special case of a miktoarm star copolymer with many arms are so-called Janus Micelles, which are formed by cross-linking the short middle block of a triblock terpolymer in the microphase separated bulk state, in which the center block self-assembles in spherical [ 189,190] or cylindrical domains [191]. By this procedure the two different outer blocks are oriented to the two opposite hemicoronas around the center block domain and subsequent dissolution leads to amphiphilic particles (Figure 14). While spherical Janus Micelles form superstructures in solution, the cylindrically shaped Janus Micelles seem to have a lower tendency of self-aggregation to higher superstructures. 

ABSTRACT. Molecular and supramolecular assemblies, some of which should be amenable to electrochemical control, have been assembled from molecular components composed of simple building blocks. Self-assembly in chemical systems appears to take place under very precise constitutional control and, in some cases, it is easier to construct the molecular and supramolecular assemblies than it is to make some of the molecular components on their own. 

When the copolymer is star shaped such as the ABC miktoarm star copolymer in which there are three different blocks (A-C blocks) with a common joint junction, the richer phase stmc-ture can be found [34,35]. When the interaction and length are the same, a symmetrical honeycomb structure can be found (Fig. 15.5a, only phases of blocks A and B are shown) and each block self-assembles into cylinder phase. The junction points are inhomogeneously distributed over the intermaterial dividing surface around cylinders formed by the respective blocks A-C. The region I shown in Figure 15.5a is the interface of different domains, which contains the mixtures of blocks A-C and star junctions. 

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