Telechelic Supramolecular Polymers

8 Poly(ethylene/butylene) with OH end groups (left), poly(ethylene utylene) functionalized with UPy units (right). Reproduced from Ref. [29] by permission of John Wiley Sons Ltd 

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J. H. K. K. Hirschbeig, F. H. Beijer, H. A. van Aert, P. C. M. M. Magusin, R. P. Sijbesma, E. W. Meijer, Supramolecular polymers from linear telechelic siloxanes with quadruple hydrogen bonded units , Macromolecules 1999, 32, 2696-2705. 

Ky Hirschberg JHK, Beijer FH, van Aert HA, Magusin PCMM, Sijbesma RP, Meijer EW. Supramolecular polymers from linear telechelic siloxanes with quadmple-hydrogen-bonded units. Macromolecules 1999 32 2696-2705. 

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... 

Figure 1.6 Schematic representation of the formation of supramolecular polymer (7) by chain extension of reactive telechelic oligomer with UPy. (After Folmer et al., 2000.)...

In all of the studies summarized above, the Mebip ligands were covalently attached to a telechelic core and served either to chain-extend or cross-link these building blocks, in connection with various metal ions, into linear or cross-linked metallo-supramolecular polymers. Rowan et al. took a different approach when they blended complexes based on monofunctional dodecyl-Mebip and metal ions into methacrylate-based polymer matrices [85]. Interestingly, when complexes with platinum ions were used, a mechanically responsive material was obtained, which... 

Another metaflo-supramolecular system, on the basis of 2,6-bis(l,2,3-triazol-4-yl)pyridine (BTP) as well as Zn and Eu ", respectively, was introduced by Weng and coworkers [95], The approach is quite different from the majority of mechanically responsive metaflo-supramolecular polymers heretofore described the ligands were designed to be part of the polymer backbone instead of being located at the end of the polymer chains. Telechelic pTHF was thus copolymerized with the dUiydroxy-functionalized BTP ligand and hexamethylene diisocyanate to produce a polyurethane that was further cross-linked through the addition of metal ions (Fig. 28a). The metal-rich domains phase-separate from the pTHF soft... 

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... 

Folmer BJB, Sijbesma RP, Versteegen RM, van der Rijt JAJ, Meijer EW (2000) Supramolecular polymer materials chain extension of telechelic polymers using a reactive hydrogenbonding synthon. Adv Mater 12(12) 874—878... 

The quadrupole hydrogen-bonded unit can be employed in the chain extension of telechelic ohgomers such as polysiloxanes, polyethers, polyesters, and polyacrbonates (Fohner et al., 2000). Thus the electrophilic isocyanate group (-NCO) of synthon (3 in Fig. 1.5) can be reacted with common nucleophilic end groups (-OH or -NH2) of telechelic ohgomers, resulting in supramolecular polymers by chain extension (Fig. 1.6). Thus the material properties of telechelic polymers have been shown to improve dramatically upon functionahzation with synthon, and materials have been obtained that combine many of the mechanical properties of conventional macromolecules... 

Figure 8 Telechelic, hydrogen-bonded supramolecular polymers described by Rowan et at ...

Figure 15 Components of a supramolecular polymer blend. Polyimide 9 contains multiple rr-electron deficient chain-folds and the telechelic polyamide 10 is end-capped with electronically complementary pyrenyl residues that intercalate into these folds. ...

Using this procedure, the reactive synthon was obtained in hundreds of grams, and was subsequently used for the functionalization of telechelic polymers. An added advantage of the use of this synthon is that it can be used to functionalize amino as well as hydroxy telechelic supramolecular... 

Clearly, supramolecular materials based on telechelics combine many of the mechanical properties of conventional macromolecules with the low melt viscosity of low molecular weight organic compounds. The reversibility of supramolecular polymers adds new aspects to many of the principles that are known from condensation polymerizations. For example, a mixture of different supramolecular monomers will yield copolymers, but it is extremely simple to adjust the copolymer composition instantaneously by adding an additional monomer. Moreover, the use of unimers with a functionality of three or more, will give rise to network formation. However, in contrast to condensation networks, the self-healing supramolecular network can reassemble to form the thermodynamically most favorable state, thus forming denser networks (Figure 6). 

In 1998, supramolecular polymers with photocontrollable molecular weights were reported for the first time (Fig. 4.10).These are formed by the self-assembly of telechelic polymers terminated into UPy units. UPy can dimerize by quadruple H-bonding with high affinity of 2.2 x 10 M in chloroform), building up long chains. A chloroform solution of this polymer (42) behaves like a solution of a conventional covalently linked polymer. 

An entirely different, but highly innovative approach to supramolecular polymers via metathesis methods has been developed by Meijer et al. (Ohkawa et al., 2007 Scherman et al., 2006a Scherman et al., 2006b) (Figure 3.11). The synthesis of biheaded telechelic PNB-polymers with H-bonds has been accomplished by Binder et al. (Kurzhals and Binder 2010) via simple crossover reactions. Based on the two selectively interacting... 

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