Polyrotaxanes solubility

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. 

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... 

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. 

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. 

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... 

CD are often more polar than the backbones on which they are threaded. Thus the solubilities of the derived polyrotaxanes are often different from those of the parent backbones, supporting evidence for the formation of polyrotaxanes. More directly, chemical shift changes of the protons of the CD upon threading are often observed [77-105]. The protons inside the CD cavity of the polyrotaxanes have different chemical shifts from those of the unthreaded species. This is because of the different chemical environment when the cavity of the CD is occupied by the linear species rather than solvent molecules. 

The solubility of a polymer will be altered by threading of the cyclic to form a polyrotaxane. The change is related to the properties and structures of both components. 

The aqueous solubility of CD also enables their potential application as poly-rotaxane-based drug carriers. Yui and coworkers incorporated CD onto PEO chains in polypseudorotaxanes and polyrotaxanes [92-94], The releasing kinetics of CD from the polymer chain were studied. The release was governed by the inclusion complexation equilibrium. Biodegradation to cleave the BG units was shown to cause the release of the CD from the polyrotaxanes. 

Gong et al. reported that the solubility of a polymeric cyclic can be altered significantly by threading with paraquat, the formation of 84 [126, 128]. Whereas polymer 83 was only partially soluble in acetone, polyrotaxanes 84 were soluble and had an orange color. Whereas polymer 83 was totally soluble in THF and paraquat was not soluble, 84 even up to min=0.971 were initially soluble except for a small amount of uncomplexed paraquat the solubility of paraquat was indeed enhanced by complexation with polymer 83. CH3CN was a good solvent for paraquat but poor for 83. However, all polyrotaxanes 84 with m n>0.428 were soluble, whereas 84 with m/n =0.232 was not this means that a certain amount of paraquat incorporation is necessary for 83 to be soluble. 

Therefore, die polarity and solubility of polymer can be modified deliberately by varying the nature of the components. High aqueous solubilities of polyamides and polyurethane threaded with crown ethers or CD are intriguing, because this observation implies potential applications of the polyrotaxane concept in coatings, adhesives, and water-borne processing. The observation of the emulsification of... 

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. 

Because of their novel topologies, polyrotaxanes have properties different from those of conventional polymers. Solubility, intrinsic viscosity, melt viscosity, glass transition, melting temperature and phase behavior can be altered by the formation of polyrotaxanes. The detailed changes are related both to the properties of the threaded cyclics and to the backbone and the threading efficiency. 

One of the structural features seen in polyrotaxanes is the absence of any covalent binding between cyclic compounds and a linear polymeric chain capped with bulky end-groups at both terminals [1]. It looks like a necklace the cyclic compounds are mechanically locked by the linear polymeric chain. The cyclic compounds in a poly-rotaxane can slide and/or rotate along the axial polymeric chain if the polyrotaxane is soluble in a certain solvent. Furthermore, such mechanical locking between the cyclic compounds and the linear polymeric chain will be opened once one of the terminal bulky end-groups is cleaved by any external conditions. These characteristics are only observable in and specific to polyrotaxanes and are never seen in conventional polymeric architectures (Fig. 1). 

Buschmann et al. were the first to prepare a polyrotaxane containing cucurbituril by cleverly adapting interfacial polymerization conditions to the requirements of the water-soluble pseudorotaxane monomer. Polymers in which cucurbituril has been threaded onto the side chain in a pseudorotaxane fashion have been reported by Kim et al. Cucurbituril has also been integrated into a branched polymer structure. Through the functionalization of the surface of a dendrimer with a diamine motif, Kim et al. achieved the threading of CB[6] onto it, leading to a pseudorotaxinated surface architecture. ... 

Poly(azomethine)-rofaxa-42-crown-14 p-tri(p-f-butylphenyl) derivatives used as blocking groups liquid crystalline Tm is 67 °C, and smectic between 67 and 73°C. Ti = 123°C. Parent polymer is insoluble polyrotaxane is soluble in chloroform, acetone, etc. [236]... 

Because of the formatiOTi of the mechanically interlocked structure, polyrotaxanes have different physical properties, such as solubility, thermostabDity, photoelectronic properties, viscosity, and phase behavior, compared with simple reference (nonpolyrotaxanated) polymers. 

A noteworthy feature of the polyurethanes of Table 43.1 is that the model polymer, the first entry, is insoluble in water, dichloromethane and acetone, whereas both the polyrotaxanes derived from 36-crown-12 and 60-crown-20 , la and Id, respectively, are soluble in these three solvents [32]. The glass transition temperatures of the polyurethane rotaxanes of Table 43.1 obey the Fox equation (see Fig. 43.1) this is due to... 

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