Supramolecular main-chain

An interesting example of how non-mesogenic rigid supramolecular main-chain polymers can affect LC environments has recently been shown [72]... 

As the gratings inscription in the H-bonded main-chain supramolecular polymer was very ineffective, the authors developed an azobenzene-containing supramolecular side-chain polymer, as it is shown in Fig. 2.4f (Gao et al., 2007a). A 300-nm deep grating was inscribed in this material under similar irradiation conditions. Note that at the same time the photoorientation ability of the azobenzene was a few times smaller than in the supramolecular main-chain polymer. The induced SRGs are thermally stable up to 120°C. A series of... 

Org. Chem., 4448 For dendronized polymers via supramolecular main chain interactions see (d) Wiirthner,... 

Furthermore, the stmctures and properties of supramolecular side-chain polymers are described. Supramolecular polymers can be divided into two classes (a) side-chain and (b) main-chain supramolecular polymers (Figure 2). Supramolecular main-chain polymers will be discussed in Chapter 6. 

Figure 6. Formation of supramolecular main-chain polymers by poly association of complementary components.

The pseudopolyrotaxane schematized in Fig. 3 has a supramolecular main-chain bond based on the dimerization of carboxyl groups. Philp and Stoddart had earlier suggested [27] that a molecular chain with appropriately spaced TT-rich rings could thread its way through several macrocycles containing n-acceptors (Fig. 9A) and subsequently be capped with large stoppers to form a permanent rotaxane polymer. The structure may be viewed as a molecular abacus with rotaxane units noncovalently linked to the molecular chain. Newer polyro-taxane polymers are described in this volume in Chapter 8. 

Fig. 6a,b. Height micrographs obtained by tapping mode SFM from monolayers of a spherical b cylindrical molecules adsorbed on mica [84]. Top self-assembly of monodendron side groups into spherical and cylindrical supramolecular dendrimers. The process depends on the degree of polymerization of the polystyrene main chain... 

MAIN-CHAIN VERSUS SIDE-CHAIN SUPRAMOLECULAR POLYMERS... 

Dramatic examples have also been reported for main-chain supramolecular polymers (SPs Lehn 1993 Ciferri 2005 Fig. 3.1), in which specific and directional molecular recognition events between end groups define the main chain of a linear polymeric assembly. Although main-chain SPs had been created and characterized previously (Broze et al. 1983 Fouquey et al. 1990 Alexander et al. 1993 Bladon and Griffin 1993 St Pourcain and Griffin 1995), it was a groundbreaking paper in 1997 that demonstrated the mechanical potential of supramolecular interactions and catalyzed much of the current interest in the field (Sijbesma et al. 1997). 

In this chapter we will focus on side chain functionalized supramolecular polymers as well as main chain noncovalent functionalized polymers, which are the two main areas of supramolecular polymers. We will initially discuss the design principles and methodology of side chain functionalization, in particular, multifunctionalization. In the later part of the chapter, we will discuss in detail two important applications of side chain functionalized supramolecular polymers. The first application involves the use of noncovalent interactions to yield highly functionalized materials, whereas the second application involves the reversible noncovalent cross-linking of polymers to yield responsive materials. 

Figure 5.2 Examples of hydrogen bonding motifs used in supramolecular polymers dimerizing uieidopyrimidone (UPy) functionalized main chain supramolecular polymers (2A), simple one-point complementary hydrogen bonding interactions between pyridine and phenol (2B), and six-point complementary hydrogen bonding interaction between cyanuric acid and the Hamilton wedge receptor (2C).

Shimizu LS. Perspectives on main-chain hydrogen bonded supramolecular polymers. Polym... 

Self-Organization of Supramolecular Liquid Crystalline Polymers from Complementary Components. If two (or more) complementary units e or 3 are grafted on a template T, mixing Te m with the complementary T3m may lead to the hetero-self-assembly of a linear or cross-linked, main-chain supramolecular copolymer species (Te m, Tsw), whose existence is conditioned by the molecular recognition-directed association between the e and a groups. 

Supermolecules built from small molecules mainly involve intermolecular interactions. On the other hand, with macromolecules the supramolecular association may be either intermolecular, occurring between the large molecules, or intramolecular involving recognition sites located either in the main chain or in side-chain appendages, thus leading to chain folding and structuration of the macromolecular... 

However, the particular synthetic requirements in the preparation of conjugated polymers have thus far severely limited the number of similarly hierarchically structured examples. Pu et al. reported different types of conjugated polymers with fixed main-chain chirality containing binaphthyl units in their backbone which exhibited, for example, nonlinear optical activity or were used as enantioselective fluorescent sensors [42—46]. Some chirally substituted poly(thiophene)s were observed to form helical superstructures in solution [47-51], Okamoto and coworkers reported excess helicity in nonchiral, functional poly(phenyl acetylenejs upon supramolecular interactions with chiral additives, and they were able to induce a switch between unordered forms as well as helical forms with opposite helical senses [37, 52, 53]. 

Similar to supramolecular polymers bearing hydrogen bonds within their main chain, side-chain architectures are possible in a similar manner. Usually,... 

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