Pseudopolyrotaxanes

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]. 

Yamaguchi, I. Osakada, K. and Yamamoto, T. (2000) Pseudopolyrotaxane composed of an azobenzene polymer and y-cyclodextrin. Reversible and irreversible photoisomerization of the azobenzene groups in the polymer chain, Chem. Commun. 1335-1336. 

The driving forces of complex formation were thought to be the geometric compatibility or fit and intermolecular interaction between hosts and guests. It has been reported that many linear polymeric guests could form inclusion complexes with CDs resulting in main-chain pseudopolyrotaxanes. When the polymers were added into the CD solutions and then sonicated, crystalline inclusion complexes precipitated. As the result of X- ray diffraction study, all crystalline inclusion complexes between CDs and polymeric guests are columnar in structure [27,43],... 

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],... 

This review has been focused on the literature relevant to pseudorotaxanes, pseudopolyrotaxanes, polyrotaxanes and rotaxanes that may potentially be used for a variety of drug delivery and medical imaging applications. 

Figure 6. Schematic representation of (a) pseudopolyrotaxanes [2a] and (b) a dendritic pseudo-polyrotaxane [15].

Most a-CD complexes of above-mentioned poly(bola-amphiphile)s are stable enough to be isolated therefore, they are classified as pseudopolyrotaxanes. Dissociation kinetics of CD pseudorotaxanes can easily be detected by following the CD concentration during dialysis or ultrafiltration, by which free a-CD rings are continuously removed, as depicted in Fig. 29. 

Fig. 31 Formation of (a-CD)n ( 3-CD)m (a-CD)n triblock pseudopolyrotaxane by sequential threading of (1) 3-CD and (2) a-CD onto 1-10,6. (filled circles, filled triangles) Coverage y (total number of anhydroglucose units of a-CD and 3-CD per repeat of 1-10,6) as a function of threading time for a-CD, (open circles) control, coverage of threading a-CD solely [276]...

The pseudopolyrotaxanes described above can be converted to polyrotaxanes by the attachment of bulky groups, which completely prevent dissociation of threaded rings. Bulky groups can be attached either (1) along the chain or (2) at both chain ends. 

First, CD polyrotaxanes were synthesized by us by polymer analogous reaction of the amino groups of the PI-ll/a-CD pseudopolyrotaxane with nicotinoyl chloride. A 25% conversion of the imino groups led to a permanent 67% coverage of... 

Gibson et al. reported that the copolymerization of poly(THF) and a diol-pseudorotaxane consisting of 4,4/-bipyridinium salt and bis-p-phenylene crown ether with diisocyanate afforded the corresponding polyurethane with the interlocked structure [48] (Scheme 6). Although this polyurethane has a pseudopolyrotaxane structure, the interlocked structure is stable because the interaction between 4,4/-bipyridinium salt and bis-p-phenylene crown ether is strong enough to keep the inclusion complex. In this elastic polyurethane, the rotaxane unit acted as a hard segment. 

It was in 1976 that Ogata et al. reported the synthesis of inclusion polyamides [78]. When /1-cyclodextrin was stirred with aliphatic diamines in water, precipitates were formed and they were characterized as inclusion compounds. Condensation of these inclusion amides with isophthaloyl or terephthaloyl chloride yielded polyamides encircled by many of the cy-clodextrins, i.e., the first pseudopolyrotaxanes. Ogata et al. likened them to a train passing through many tunnels . The solubility and water absorption of the pseudorotaxanes were greater than those of the naked polymer threads. Differential thermal analysis experiments showed that the thermal properties of the pseudorotaxanes were different both from the naked threads and from /1-cyclodextrin. 

Maciejewski s group reported a series of papers which described several attempts at the preparation of pseudopolyrotaxanes in the solid state [79-83]. For example, the radiation polymerization of the crystalline adduct of vinylidene chloride and /1-cyclodextrin yielded a pseudopolyrotaxane, in which one cyclodextrin occupied 2.9 repeat units of vinylidene chloride [80],... 

Urethane-forming reaction between isocyanate and hydroxyl group was utilized by Osakada et al. to prepare polyurethane-cyclodextrin pseudoro-taxanes (Scheme 15) [86]. Polyaddition of a diol and MDI in the presence of permethylated a-cyclodextrin or permethylated (5-cyclo dextrin was carried out in DMF for 20 h at 120 °C to yield the pseudopolyrotaxane. The molar... 

Ito and co-workers prepared pseudopolyrotaxanes from polyaniline with emeraldine base and /f-cyclodextrin, which were studied by frequency-do-main electric birefringence (FEB) spectroscopy in a solution of N-methyl-2-pyrrolidone (NMP), scanning tunneling microscopy, etc. [120, 121]. The FEB results showed that polyaniline in the solution with cyclodextrin changed its conformation from coil to rod at low temperature below 275 K. Some rod-like structures were observed on a substrate by STM. Thus, the pseu-... 

Although Meschke et al. claimed that the pseudopolyrotaxane was obtained, the existence of pseudopolyrotaxane structure is still unclear because of the lack of the attractive interaction between polymer and cucurbituril. 

Pseudopolyrotaxane was synthesized via threading of poly(4,4 -bipyri-dinium salt) into cucurbituril in water (Scheme 27) [174]. In the complex,... 

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