2- -polyrotaxanes

The chemistry of rotaxanes has progressed well in accordance with the interest in their unique structures and the expectation of development as parts of molecular machines and molecular devices. It was in 1976 that Ogata et al. [69] reported the synthesis of the inclusion complex with polyamide. When /3-CD was stirred with aliphatic diamines in water, precipitates were 

Ripmeester et al. [117] have investigated the single crystal structural analysis of PEG and y0-CD (Fig. 27). The crystals of y0-CD-PEG inclusion com- 

The authors also studied pset/do-rotaxane formation of CDs with aliphatic polyesters, polydiene, polysiloxane, and polysilane, as summarized in Table 2. CDs were found to form inclusion complexes with aliphatic polyesters, such as PTA, PBA, PEA [107], and P(e-CL) [108,109]. a- and y-CDs formed complexes with these polyesters in high yields, although p CD gave complexes in moderate yields. Although the yields of the complexes of a-CD with PTA and 

PBA decreased with increasing molecular weight, a-CD formed complexes with PEA in high yields even at higher molecular weights. a-CD-P(g-CL) complexes were stoichiometric one-to-one (CD monomer unit) compounds, and y-CD-P(e-CL) complexes were one-to-two compoimds when the molecular weights of P(fi-CL) are low. 

Tonelli et al. [121] also reported complex formation of a-CD with PEG without solvent. Takata et al. [122] reported the preparation of polyrotaxanes from complexes of a-CD with THE in a similar way. 

The above condensation reactions were carried out at 180-200°C in aromatic solvents [250]. 

Preparation of polymeric materials that consist of linear structures threaded through large rings (see Chap. 1) has intrigued many. The result is that various publications have appeared in the literature describing such preparations [252, 253]. In many instances, crown ethers are used to have 

7 Step-Growth Polymerization and Step-Growth Polymers 

The degree of threading was found to increase with increasing molar feed ratio of crown ethers to the polymeric NH groups [255]. 

Polymeric rotaxanes were reviewed recently by Harada et al. 

As depicted in Fig. 12, rotaxanes are composed of a dumbbellshaped component, in the form of a rod and two bulky stopper groups, around which there are encircling macrocyclic component s) [310]. The stoppers of the dumbbell prevent the macro-cycle(s) from unthreading from the rod. 

After electropolymerization, the film could be demetalated (using CN or SCN ) without modification of the geometrical shape of the preformed complexing cavities, and other metals could be incorporated, such as Co(II), Zn(II), Ag(I), and Li(I). Consequently, the possibility of replacing a transition metal with another one appears to be of great interest in the applications in cata is of homogeneous organic reactions. 

The functionalized PPy films deposited on an electrode surface showed the characteristic electrochemical response of both the redox centers and the conjugated polymer. In contrast, any contribution of the incorporated metal to electron conductivity was not observed. With the same strategy, other polyrotaxane-like networks have been electrosynthesized from an intertwined het-eroleptic cobalt complex (23) [320], The spectroscopic and electrochemical properties of this complex were reported to be veiy similar to those of the homoleptic series 22. 

When a macrocycle containing two different chelating units, namely 2,9-diphenyl-l,10-phenanthroline and 2,2 6, 6 -terpyri-dine, was used, electrochemically induced molecular motions 

Other polyrotaxanes containing a thiophene-based conjugated backbone have been synthesized from the Cu(I)- or Zn(II)-driven assembly between a macrocyclic phenanthroline and a bithiophene-substituted phenanthroline [322] or bipyridine [323, 324]. Swager and co-workers have demonstrated that the contribution of the metal ion to the electronic properties of the polyrotaxane was possible when more electron-rich 3,4-(ethylenedioxy)thio-phene groups were used in place of thiophenes in the polymer backbone [324]. So a 10 -10 -fold increase in the polymer s conductivity was observed after poly(24) was treated with Cu(II) solution. This result was ascribed to the oxidation of the poly(24) backbone by Cu ions to generate poly(24,Cu) with charge carriers in the polymer backbone. 

---

Scheme 1. Schematic representations of a [2]rotaxane, a [2]pseudorotaxane, and one-, two-and three-dimensional polyrotaxanes...

A polyrotaxane with a dendrimer-like structure is known [60]. Based on the observation that [3-CD and sodium deoxycholate (NaDC) 54 forms a 2 1 host guest complex in water, Tato et al. constructed hyperbranched polyrotaxanes 55 by slowly reacting triply branched receptor 53 containing P-CD and NaDC... 

Dendritic Polyrotaxanes Incorporating Ring Components at Branching Points Type lll-B... 

Fig. 19. (a) Divergent and (b) convergent synthesis of dendritic polyrotaxanes with mechanical branching units... 

Fig. 21. Dendritic polyrotaxanes with mechanical branching units containing covalently linked bis-dendrons and a core imit fused to polyether macrocycles...

Takata, T., Kihara, N. and Furusho, Y. Polyrotaxanes and Polycatenanes Recent Advances in Syntheses and Applications of Polymers Comprising of Interlocked Structures. Vol. 171, pp. 1-75. 

Fujita, H Ooya, T. and Yui, N. (1999) Thermally induced localization of cydodextrins in a polyrotaxane consisting of (3-cydodextrins and poly (ethylene glycol)-poly(propylene glycol) triblock copolymer. Macromolecules, 32, 2534-2541. 

Polyrotaxane Containing Monodisperse Oligo(ethylene glycol). 183... 

Gibson et al. [109] and Sjen et al. [110] reported pseudo-polyrotaxanes and polyrotaxanes consisting of crown ethers with various polymers. The resulting polyrotaxanes were nonstoichiometric. Their properties - including solubility and glass transition temperatures - were different from those of the starting polymers. 

Harada et al. were the first to synthesize a polyrotaxane. Using the process shown in Scheme 1, they obtained an inclusion compound in which many a-CDs are threaded by a PEG chain and named it molecular necklace . Wenz et al. [132] reported polyrotaxanes containing polyamines and a-CDs. Because of its significance and interest, the approach used by Harada et al. to obtain the molecular necklace is worth reproducing here in some detail. 

Harada et al. started from preparing inclusion complexes by adding an aqueous solution of PEG bisamine (PEG-BA) to a saturated aqueous solution of a-CD at room temperature and then allowing the complexes formed to react with an excess of 2,4-dinitrofluorobenzene. They examined the product by column chromatography on Sephadex G-50, with DMSO as the solvent, and obtained the elution diagram shown in Fig. 46. They identified the first, second, and third fraction, respectively, as the desired product, i.e., a polyrotaxane, dinitrophenyl derivatives of PEG, and uncomplexed a-CD, by measurement of both optical rotation and UV absorbance at 360 nm for the first, UV absorbance at 360 nm for the second, and optical rotation for the third. 

The polyrotaxane fraction was insoluble in water and DMF, but soluble in DMSO and 0.1 N NaOH. Its XH NMR spectrum- shown in Fig. 47, together with those for the second and third fraction- indicates that the polyrotaxane consists of CD, PEG-BA, and dinitrophenyl groups and that all peaks are broadened by complexation, which implies that a-CD rings become less mobile when including PEG. 2D NOESY NMR spectra showed that the H-3 and H-5... 

Table 5. Polyrotaxanes prepared from PEG-BA with various molecular weights...

Polyrotaxane Molecular weightb Number of ethylene glycol units (included + non-included) Number of threaded a-CDb Molar ratio of ethylene glycol units to a-CD... 

These end groups were removed by cleaving the C-N bond with a strong base (25% NaOH) so that the CD rings may slip off the polymer chains, and the number of CDs per polyrotaxane was estimated by H NMR, optical rotation, and UV absorption to be 12. This figure indicates that nearly the entire length of the 28 mer PEG chain was covered with CDs, because, as repeatedly noted above, the stoichiometric ratio for the complexation between PEG and a-CD is 2. 

Harada and coworkers proceeded further to obtain a tubular polymer from a PEG-a-CD polyrotaxane by using Scheme 2. The polyrotaxane was prepared... 

The molecular tube was soluble in water, DMF, and DM SO, though the unbridged polyrotaxane was insoluble in the first two. Its H NMR spectra in D20 and DMSO-d6 and its 13C NMR showed the presence of both bridged and unbridged CDs. The H NMR peak was broader for the bridged CD than for the unbridged one, and this was an additional indication that the tube is polymeric. 

---