Main-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). 

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).

Utilization of the single hydrogen bond between pyridine and benzoic acids in SLCP s has been a source of inspiration for other groups in the development of main-chain supramolecular polymers based on diacids and dipyridines.53-56 Supramolecular rod-coil polymers have been developed by assembly of 4,4 -bipyridines and telechelic polypropylene oxide with benzoic acid end-groups, which show highly ordered liquid crystalline phases.57 The use of tartaric acid derivatives in combination with bipyridine units resulted in the formation of hydrogen-bonded, chiral main-chain LCP s, as has been shown by circular dichroism measurements, optical microscopy, and X-ray data.58,59... 

Fig. 7. Formation of main-chain supramolecular polymers by polyassociation of complementary components. R and Rj represent different subunits fitted with recognition groups a variety of such groups may be used. Cross-linking components may also be introduced. The process is instructed, dynamic, and combinatorial.

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... 

Figure 1 Side-chain and main-chain supramolecular polymers of varying architecture linear polymers and cross-linked polymCT networks. (Reproduced from Ref. 16. Wiley-VCH, 2001.)...

Fox JD, Rowan SJ (2009) Supramolecular polymerizations and main-chain supramolecular polymers. Macromolecules 42(18) 6823-6835. doi 10.1021/ma901144t... 

In main-chain supramolecular polymers, noncovalent interactions are used to form the polymer chain, which consists of bi- or multifunctional molecules (monomers) that bind to each other noncovalently to form polymers (linear when bi-functional monomers are used, branched polymers or networks for multifunctional monomers). Besides monomers, end-group-functionalized polymers can also be used as supramolecular macromonomers. Such polymers can then create block copolymers [8]. 

The basic characteristics of main-chain supramolecular polymers are presented schematically in Figure 16. Designating the monomer core residues by R monomers bearing two identical interaction/recognition groups (homoditopic), may yield either homopolymers, when Rj regularly alternating copolymers when Rj R . 

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 2 Schematic illustration of two classes of supramolecular polymers (a) side-chain supramolecular polymers (b) main-chain supramolecular polymers.

Hydrogen-Bonded Main-Chain Supramolecular Polymers Constructed by Low-Molecular-Weight Monomers... 

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