Polyrotaxanes crown ether-based

Yui s group found the thermal stability of their biodegradable polyrotaxane was better than that of the separate components, poly( -lysine) and a-cyclodextrin [12,13]. In some crown ether based systems, as shown below, thermal stabihty decreases because of the lability of the cyclic components. 

On the other hand, to constrain the cyclic, the blocking group (BG) has to be bulkier than the cavity of the cyclic molecule. Harrison found that a trityl group can only block cyclics up to 28-membered whereas the tris(p-t-butylphenyl)-methyl moiety can effectively constrain 42-membered cyclics [3, 13, 14]. These results have been widely applied as a guide in the preparation of polyrotaxanes e.g., monofunctional [18, 19] and difimctional [19—23] BG based on tri- and tetra-arylmethane derivatives were successfully prepared and used as end groups and in-chain units, respectively, to constrain crown ethers in a variety of polyrotaxanes. 

Most of the reported polyrotaxanes are based on CD and crown ethers. Only a few polyrotaxanes are from other macrocycles, e.g. phenanthroline-based cyclics and bisparaquat cyclophane. Most CD-based polyrotaxanes were prepared by threading CD on to preformed polymers because CD are only soluble in polar solvents or water and not compatible with typical polymerization conditions. On the other hand, aliphatic crown ethers are soluble in water and most organic solvents. Therefore, they have broadened the scope of polyrotaxanes in terms of both polymerization conditions and types of backbones. They have often been threaded onto polymeric backbones by using them as solvents during polymerizations. 

A fascinating self-assembly process is based on the spontaneous threading of cyclodextrins or crown ethers onto polyether polyamine" or polyurethane chains (Figure 5.30). The formed polyrotaxanes possess several cyclodextrin units which are trapped after appropriate capping of the ends. Polymerization of the threaded cyclodextrins and removal of the central thread then leads to molecular cyclodextrane tubules with an inner hydrophobic tunnel and a diameter of about 5 A. 

Polyrotaxanes, in which many cyclic molecules are mechanically interlocked onto a polymeric chain, have been synthesized using macrocyclic compounds such as cyclodextrins, crown ethers and blue boxes. Synthesis of pillar[5]arene-based polyrotaxanes consisting of cationic polymers, such as viologen polymer, is relatively easy because pillar[5]arene forms stable host-guest complexes with cationic molecules (see details in Chapter 9) however, it is difficult to synthesize nonionic polymer-based polyrotaxanes. To synthesize nonionic polymer-based polyrotaxanes, we used a liquid... 

In conclusion, ILs can act as guests to form supermolecules with several kinds of host molecules (i.e., cyclodextrins, cucurbit[n]urils and calixarenes), and can participate the constructing of supramolecular assemblies (i.e., micelles, microemulsions, lyotropic LCs, vesicles and gels). Besides, ILs can affect the formation of supramolecular structures, for example, the formation of polyrotaxanes and polypseudorotaxanes, the formation of the supramolecular structures in the extraction systems based on crown ethers, and so on It is... 

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