Polyrotaxane cyclodextrin

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

Supermolecular interlocked macromolecules have been paid much attention as candidates of smart materials. Polyrotaxane (PRX) is a typical example. PEG/ cyclodextrin (CD)-based polyrotaxane was firstly reported by Harada and coworkers by attachment of stoppers to pseudopolyrotaxane (pPRX) consisting of a PEG and CDs [263]. Subsequently, many CD-based PRXs have been designed and prepared as smart materials such as biomaterials, light-harvesting antennae, insulating polymers, stimuli-responsive molecular shuttles etc. [264—268]. 

Anderson and coworkers [183-185] reported water-soluble polyrotaxanes 149 and 150, containing sulfonated PPV chains surrounded by mechanically bound a- and (3-cyclodextrin macrocycles (Chart 2.32). The cyclodextrin rings play the role of a wire insulator, preventing aggregation and interchain quenching. The effect was demonstrated by atomic force... 

F. Cacialli, J.S. Wilson, J.J. Michels, C. Daniel, C. Silva, R.H. Friend, N. Severin, P. Samori, J.P. Rabe, M.J. O Connell, P.N. Taylor, and H.L. Anderson, Cyclodextrin-threaded conjugated polyrotaxanes, as insulated molecular wires with reduced interstrand interaction, Nat. Mater., 1 160-164, 2002. 

Polymers are generally not discussed in this book. However, a polymer with rotaxane structures involving cyclodextrins in side chains 408 [36], pseudorotaxane superstructures [37], doubly twisted polyrotaxane [38] as well as infinite polyrotaxane network (Figure 8.2.5) [39] can be mentioned here. 

Research Focus Method of preparing viscoelastic polymers using crosslinked polyrotaxane inclusion complexes consisting of polyethylene glycol (PEG)-carboxyhc acid and a-cyclodextrin. 

Preparation of crosslinked polyethylene glycol a-cyclodextrin polyrotaxane... 

A higher degree of divinylsulfone crosslinking was observed in the comparative sample because of the absence of O-methylation of a-cyclodextrin polyrotaxane. 

Nakajima et al. (1) prepared liquid crystalline polyrotaxane derivatives containing the mesogenic group 4-cyano-4 -hydroxybiphenyl attached to the a-cyclodextrin component of linear polyethylene glycol containing an a-cyclodextrin inclusion complex with an adamantane termini. 

Polyrotaxanes have been prepared by threading multiple a-cyclodextrin units onto a bulky benzimidazole-based linear chain polymer with an aliphatic spacer where the cyclodextrin resides. The rotaxane forms as the cyclodextrin-bound precursor amine is polymerised. Compared to the polymer in the absence of the cyclodextrins, the glass transition temperature is raised by some 20 °C even though only ca. 16 % of the aliphatic spacers in the polymer are rotaxanated.28 A novel approach to polyrotaxanes involved the use of a metal ion such as Zn2+ to thread a phenanthroline-based macrocycle onto a thiophene-based complementary monomer. The resulting pseudorotaxane can then be electropolymerised and the Zn2+ ions removed to give a polyrotaxane, Scheme 14.5. The redox and conductivity properties of the polymer are very much dependent on whether a metal ion is bound or not.29... 

Yamaguchi, I., Osakada, K., Yamamoto, T., Polyrotaxane containing a blocking group in every structural unit of the polymer chain. Direct synthesis of poly(alkylenebenzimidazole) rotaxane from Ru complex-catalyzed reaction of 1,12-dodecanediol and 3,3-diaminobenzidine in the presence of cyclodextrin. J. Am. Chem. Soc. 1996, 118, 1811-1812. 

It has been also reported a study on the threading process of a a - cyclodextrin (a-CD) and polyethylene glycol (PEG), as a function of temperature and solvent composition. This reaction produces a polyrotaxane that eventually precipitates and forms a thick gel. Ceccato et al. [46] have proposed a molecular model for the interpretation of the temperature and solvent composition effect on the threading process. According of this model, the reaction can be depicted as a five - step phenomenon that mainly depend on the threading and sliding of a-CD and PEG. The transition... 

Due also to their controllable size, low cytotoxicity, and unique architecture, cyclodextrin-based polyrotaxanes and pseudopolyrotaxanes have been developed to encompass a broad range of diverse medical applications from erodable hydrogels to drug and gene delivery. A recent review about biomedical applications of cyclodextrin based polyrotaxanes have been reported by Loethen et al. [64],... 

Further examples of the alternate organic/inorganic adsorption include combinations with cyclodextrin, polyrotaxane, and dendrimer, which play an... 

Figure 32 (a) Preparation of polyrotaxanes by threading of a-cyclodextrine on the macromolecular chain, (b) Rate of threading as determined... 

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. 

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