Polyrotaxane

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. 

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