Advancements in Synthesis & Applications of Polypseudorotaxanes & Polyrotaxanes: A Review, Study notes of Conflictology

Download Advancements in Synthesis & Applications of Polypseudorotaxanes & Polyrotaxanes: A Review and more Study notes Conflictology in PDF only on Docsity! Chapter 1 Polypseudorotaxanes and Polyrotaxanes 1.1. INTRODUCTION As implied by their names, polypseudorotaxanes/polyrotaxanes1 are constructed simply by incorporating pseudorotaxane/rotaxane moieties into polymers. According to how the cyclic and linear units are connected, different kinds of polypseudorotaxanes and polyrotaxanes can be made; those that have been studied up to now or are possible are summarized in Figure 1. Depending on the location of the pseudorotaxane/rotaxane unit, polypseudorotaxane/polyrotaxanes can be divided into two types: main chain polypseudorotaxanes (A and B in Figure 1)/polyrotaxanes (E-I in Figure 1), in which the pseudorotaxane/rotaxane unit is a part of the main chain, and side chain polypseudorotaxanes (C and D in Figure 1)/polyrotaxanes (J and K in Figure 1), in which the pseudorotaxane/rotaxane unit is a part of the side chain. 1 n n n n n H I E F E-I: Main-Chain Polyrotaxanes J&K: Side-Chain Polyrotaxanes G n A n B n n C J A&B: Main-Chain Polypseudorotaxanes C&D: Side-Chain Polypseudorotaxanes n n K D Figure 1. Various types of polypseudorotaxanes and polyrotaxanes. 2 n n E G n A n B Route I: n n + Route II: 2 2n n H Route III: F n n n+Route IV: n 2n n Route V: Route VII: n nn + or + n nn + n n Route VI: I n nRoute VIII: F n Scheme 1. Synthetic routes for main chain polypseudorotaxanes and polyrotaxanes. 5 Cyclodextrins (CDs), extensively studied as host molecules in polypseudorotaxanes and polyrotaxanes, are a series of cyclic oligosaccharides of 1,4- linked D(+)-glucose units.2 The three most commonly used CDs are α-, β-, and γ-CD. They have a cylindrical cavity having a depth of ca. 7.0 Å and an internal diameter of ca. 4.5 Å for α-CD, ca. 7.0 Å for β-CD, and ca. 8.5 Å for γ-CD.2 These cylindrical cavities possess hydroxyl functionalities on the two rims and hydrocarbon and ether moieties in the interior of the cavity. Therefore CDs have a hydrophobic interior and hydrophilic external faces. The typical linear species used to form inclusion complexes with CDs have two hydrophilic ends and a hydrophobic middle part. When a guest like this and a CD dissolve in water or a polar solvent, the hydrophobic part of the guest species will insert inside of CD while the hydrophilic parts will stay outside to produce an inclusion complex. Therefore, the formation of these inclusion complexes is a result of CDs’ geometry and functionality. O OH X HO O OH Hydrophilic X = 6, α-CD, X = 7, β-CD, X = 8, γ-CD Hydrophobic = Yamaguchi et al.3 used route I to synthesize a polyrotaxane by reacting 3,3’- diaminobenzidine and 1,12-dodecanediol in the presence of α-CD and RuCl2(PPH3)3. The aromatic rings incorporated along the polymer backbone are far too bulky to pass through the relatively small cavities of the α-CDs. As a result, the macrocyclic components are trapped on the aliphatic portions of the polymer and cannot even travel along the backbone of the acyclic component. This polyrotaxane contains a blocking group in every structural unit of the main chain, as shown in Figure 2. 6 H2N H2N NH2 NH2 HO (CH2)12 OH+ RuCl2(PPh3)3 1 : 3 : 0.5 Alpha-CD+ (A)l (B)m (C)n l : m : n = 16 : 84 : 0 (CH2)11 O (CH2)11 IA: (CH2)11 O (CH2)11 IB: (CH2)11 IC: H N N N N H I = = Alpha-CD Figure 2. Polyrotaxane containing a blocking group in every structural unit of the polymer chain. Wenz and Keller4a,b empolyed route II to prepare some main chain polyrotaxanes based on α-CD. In these polyrotaxanes, the steric barrier provided by the pyridyl rings traps the α-CD rings mechanically on the linear component. Later they made some other polyrotaxanes based on β- and γ-CD.4c The formation of the tetraphenylenecyclobutane blocking groups along the backbone of 4 was achieved by irradiating aqueous solution of 3, which self-assembles spontaneously from its separate components, 1 and 2, in the presence of both β- and γ-CD (Figure 3). 7 accessibility of a membrane-bound zinc metalloexopeptidase to the terminal peptide moiety. This finding will provide a new design of polymers with controlled degradation profile for biomedical applications. Some other polyrotaxane-related structures with potential biological applications, such as drug delivery, were prepared by this group.12 HO (CH2CH2O)a (CH2CHO)b CH3 (CH2CH2O)a H THF O (CH2CH2O)a (CH2CHO)b CH3 (CH2CH2O)a C O C O N N NN O (CH2CH2O)a (CH2CHO)b CH3 (CH2CH2O)a C O C O N N CH2CH2NH2H2NH2CH2C H H O (CH2CH2O)a (CH2CHO)b CH3 (CH2CH2O)a C O C O N N CH2CH2NH2H2NH2CH2C H H O N COOH O HO DMF O (CH2CH2O)a (CH2CHO)b CH3 (CH2CH2O)a C O C O N N CH2CH2NH H H NHCH2CH2 N,N'-ca C S rbonyldiimidazole Ethylenediamine Beta-CD 0.1 M Phosphate buffered saline ... ... O NH C OHO S HOOC O NH C COOH O OH S ... ... Figure 4. Synthesis of a polyrotaxane consisting of β-CD and poly(ethylene glycol)- poly(propylene glycol) triblock copolymer. 10 NH (CH2)4 CH CO NH2 2n Alpha-CD NH (CH2)4 CH CO NH2 n NH (CH2)4 CH CO NH2 Figure 5. Synthesis of a main-chain polypseudorotaxane based on poly(ε-lysine) and α- CD. The interaction between the CD-based polyrotaxanes and the surrounding water molecules plays an important role on the mechanical properties and reactivity of polyrotaxanes in aqueous solutions. Sano’s group used Raman intensity of the collective band to study the order of the structure of water molecules in order to clarify this type of interaction.13 Recently, people have become interested in carbohydrate-displaying pseudopolyrotaxanes and polyrotaxanes of CDs threaded onto linear polymer chains as dynamic multivalent neoglycoconjugates.14 Yui and coworker studied α-CD-based poly(ethylene glycol) polyrotaxanes displaying variable amounts of maltose residues in a concanavalin A hemagglutination assay.14a The Stoddart group prepared α-CD-based pseudopolyrotaxanes displaying lactosides for binding to lectins.14b,c All these studies demonstrated that the formation of supramolecular structures, like polypseudorotaxanes and polyrotaxanes, could enhance protein-carbohydrate interactions in a dynamic multivalent way. Lo Nostro et al. studied the kinetics of the threading of CDs onto linear polymers, α-CD onto PEG15a and β- & γ-CD onto PPG.15b,c They found that the threading was favored by low temperature and solvents with a strong hydrogen bonding network (D2O > H2O > urea). A model was proposed to interpret the temperature and solvent composition effect on the threading process. Furthermore, transition state theory was used to calculate the Gibbs free energy change (∆G) related to this process and the number of α-CD molecules that participated in the formation of the three polypseudorotaxanes. It was found that ∆G changes little with temperature. An enthalpy/entropy compensation was found in these systems. They studied the effect of 11 salts on the threading process for a polypropylene glycol derivative with β-CD. Changes in the threading time are strongly dependent on the nature of both cations and anions. They demonstrated that the diversity of salt effects is related to the microscopic frequency dependent dielectric properties of the ion pair, which account for the dispersion potential experienced by the different ions in solution. Recently they found that threaded α-CD rings on PEG polymer chains form wormlike aggregates ("poly-CD") in water solutions.15d Tait and Davies15e studied the kinetics of polypseudorotaxane formation between the cyclodextrin and poly(ethylene glycol) dimethyl ether (DMPEG) using the lag time approach. They found that the inclusion of poly(ethylene glycol) by α- CD is mainly driven by the precipitation of the polypseudorotaxane. Though α-CD has been found not be able to form polypseudorotaxanes with PPG,15b,c it can form polypseudorotaxanes with a PEG-PPG random copolymer15f and PPG-PEG-PPG triblock copolymers15g as shown by works done by Li and coworkers. The kinetic studies of these inclusion complexes revealed that the threading time is strongly dependent on the PPG block lengths, because the α-CD molecules have to first overcome the energy barrier to slide over the PPG blocks before forming stable complexes with the middle PEG block.15g Harada and coworkers16 reported the synthesis of the first molecular tube (MT) by crosslinking adjacent hydroxyl groups on α-CDs in a polyrotaxane in 1993. Because of the MT’s large and hydrophobic cavity, it can form inclusion complexes with guest molecules containing a long hydrophobic segment. One MT recently made by Yui’s group17 is shown in Figure 6. First α-CDs were threaded onto α,ω-diamino poly(ethylene oxide) to form a polypseudorotaxane, 5. Then 5 was capped to produce a polyrotaxane 6. Hydroxyl groups adjacent to the α-CDs on 6 were crosslinked by epichlorohydrin to form 7. At last the dinitrophenyl groups at the ends of 7 and the linear polymer backbone were removed to form the MT, 8. This group studied thermodynamics involved in the inclusion complexations of the MT with sodium dodecyl sulfate (SDS)17a and sodium alkyl sulfonates (CnSO3Na).17c They found that the inclusion complex between MT and SDS was more stable than that between α-CD and SDS. Each MT was observed to form the inclusion complex with two guest molecules, SDS or CnSO3Na with different alkyl chain lengths. Enthalpy/entropy compensation was also found in the two systems. The 12 They found that α-CD did not complex with PDMS, but β- and γ-CD did. Shigekawa and coworkers23c demonstrated that the movement of α-CDs in a α-CD/PEG polyrotaxane could be manipulated by the tip of a scanning tunneling microscope. Recently Harada and coworkers used the photodimerization of terminal anthracene groups to prepare a series of main-chain polyrotaxanes.24a-c They prepared a poly(polyrotaxane) from photoreaction of a 9-anthracene-capped polyrotaxane (Figure 7). In this process, first the inclusion complexation between α-CD and PEG with one end capped with 9-anthracene produced a semi-polyrotaxane, which was capped using 9- anthracenecarboxylic acid to give a polyrotaxane. Exposure of this polyrotaxane to visible light afforded a poly(polyrotaxane) by cyclodimerization of the terminal anthryl moieties. This poly(polyrotaxane) can be converted into the starting polyrotaxane by irradiation with UV light or heating. Later they prepared a polyrotaxane by photoreactions of a precursor complex between β-cyclodextrin with PPG having a triphenylmethyl group at one end and a 2-anthryl group at the other end.24b A similar method was used in the fabrication of polyrotaxanes based on γ-CD and PPG.24c 15 CH2 NH CH2CH2O CH2CH2 NH2n alpha-CD / Water CH2 NH NH2 n -2 OH N N N OH TEA, EDA / DMF, , m NH n m CH2 NH heat or UV light hv (visible light) n m + poly(polyrotaxane) poly(catenane) Figure 7. Preparation of a poly(polyrotaxane) by photoreaction. Molecular dynamics simulations were performed by Pozuelo et al.25 for polyrotaxanes formed by PEG and α-CD. The number of α-CDs the polymer can capture is limited by its length. The main source of stabilization of these polyrotaxanes is van der Waals interactions. Hydrogen bonding between adjacent α-CDs slightly favor head-to- head, tail-to-tail sequences over head-to-tail sequences (this conclusion agrees with the polyrotaxane made by Yui’s group shown in Figure 4). The α-CDs in polyrotaxanes are more symmetric and less distorted than the isolated α-CDs. The PEG in the polyrotaxane 16 is more extended than an unperturbed chain, because it has a larger population of trans states at the internal bonds. Hwang and coworkers26 demonstrated that the threading following by recrystallization methodology might be a simple route to prepare a well-defined polymer structure on a micrometer scale by production of hexagonal microfibers from recrystallization of a α-CD/PEG polypseudorotaxane in water. 1.3. MAIN-CHAIN POLYPSEUDOROTAXANES AND POLYROTAXANES INCORPORATING CROWN ETHERS Crown ethers are macromonocyclic polyethers. They have been widely studied as hosts for organic salts, such as secondary ammonium salts27 and paraquat derivatives.28 In the past ten years Gibson’s group was active in the preparation of main chain polyrotaxanes incorporating crown ethers.29-44 They have utilized crown ethers to synthesize a variety of polypseudorotaxanes and polyrotaxanes.29-40 By carrying out step- growth polymerizations in the presence of unfunctionalized crown ethers, main chain polyester29,30 and polyurethane31,32 polypseudorotaxanes of Type A (Scheme 1) were prepared. By use of bulky monomers in step-growth polymerizations in the presence of unsubstituted crown ethers, as exemplified by the preparation of poly(ester rotaxane)s33,34 and poly(urethane rotaxane)s,35 polyrotaxanes of Type F resulted. Reaction of poly(methacryloyl chloride) with 5-hydroxymethyl-1,3-phenylene-1’,3’-phenylene-32- crown-10 resulted in highly branched or crosslinked polymers of Type H, depending on the solvent and concentrations, as a result of self-association of the crown ether via hydrogen bonding and subsequent self-threading of the crown ether moieties.33a Poly(styrene rotaxane)s36 and poly(acrylonitrile rotaxane)s37 of Types A and F resulted from chain-growth polymerizations. Main chain poly(acrylate rotaxane)s and poly(methyl methacrylate rotaxane)s of Type A were also prepared using free radical polymerization.38 Main-chain polypseudorotaxanes of Type B have been investigated by this group.39 The statistical threading method (route II in Scheme 4) was employed to prepare polyrotaxanes based on polystyrence.36a Here a free radical initiator carrying a bulky 17 O O O O O O O O O O OH HO N N O O O O O O O O O O OOCCH3 OOCH3C CH3COCl PF6 -PF6 - OHHO O O O O O O O O O O OOCCH3 OOCH3C ClCO(CH2)8COCl O O O O O O O O O O CH2OCO(CH2)8COOCH2 + + ++ Acetone n ++ Acetone O O O O O O O O O O CH2OCO(CH2)8COOCH2 n Figure 10. Synthesis of a polyester main chain polypseudorotaxane Beckham’s group prepared some main-chain polyurethane-based polyrotaxanes from hexamethylene diisocyanate and either ethylene glycol or diethylene glycol in crown ether solvents.46 It was found the threading efficiency increased with increasing crown ether ring size. 1.4. SIDE-CHAIN POLYPSEUDOROTAXANES AND POLYROTAXANES Side-chain polypseudorotaxanes and polyrotaxanes can be prepared by the routes in Scheme 2. In route i macrocyclic components are threading onto the side chains of an existing polymer to get the polypseudorotaxane. Then stoppers are introduced to obtain polyrotaxanes. Route ii involves the reactions between the functional groups on [n]- pseudorotaxanes and the functional groups on the side chains of the polymer. Linear components in route iii are threaded into the macrocycles on the side chains of a polymer 20 to produce a polypseudorotaxane of type D and then stoppers are introduced to get a polyrotaxane of type K. In route iv, the functional groups on the rotaxanes react with the functional groups on the side chain to afford a polyrotaxane of type K in Figure 1. In routes v-viii, the homopolymerization of a pseudorotaxane or rotaxane monomer leads to the formation of a polyrotaxane of type J or K in Figure 1. 21 Z Z X Z C J K Y X Z X Y X Y X Y J YX K n n n n n 2n n n n n Route iii: Route i: n n Route ii: n n Route iv: n n nor n nor n Route v: Route vi: X Y n nor n C D n YX n nor Route vii: Route viii: D Scheme 2. Synthetic routes for side chain polypseudorotaxanes and polyrotaxanes. 22 O O O O O O O O O O 9 1 n H3C N + N+ CH3 PF6 - PF6 - ++ + m = O O O O O O O O O O ++ n Figure 12. Preparation of a side-chain polypseudorotaxane. Takata and coworkers52a made side-chain polypseudorotaxanes by radical homopolymerization of semirotaxanes consisting of a crown ether wheel and acrylate axle bearing a bulky end-cap and ammonium group (route v in Scheme 2). Gibson’s group also prepared side-chain polypseudrotaxanes52b of type D in Figure 1 and polyrotaxanes52c of type J in Figure 1 with crown ethers as the macrocylic components. Yamaguchi et al.53 synthesized a novel side chain polyrotaxane by N-alkylation of poly(benzimidazole)s with the appropriate semirotaxanes composed of a trimethyl- cyclodextrin encircling a linear component bearing a bulky trityl group at one end and a bromide leaving group at the other. These polyrotaxanes have much higher solubility in organic solvents than their parent polymers. 1.5. OTHER POLYPSEUDOROTAXANES, POLYROTAXANES, AND RELATED STRUCTURES Cucurbituril (Figure 13) is a hexameric macrocyclic compound. Although the size of its cavity is similar to that of α-CD, its highly symmetrical structure with two identical openings distinguishes it from α-CD and the polar carbonyl groups at the portals allow it to bind ions and molecules through charge-dipole and hydrogen-bonding interactions.54 Cucurbituril has been applied to construct a variety of polypseudorotaxanes and polyrotaxanes by Kim’s group by the combination of self-assembly and coordination chemistry.55 For these systems, a stable pseudorotaxane was formed first by threading a cucurbituril with a short linear molecule and then metal ions were used as linkers to 25 organize the resultant pseudorotaxanes into one-dimensional and two-dimensional polypseudorotaxanes and polyrotaxanes. The overall structure of a polypseudorotaxane or a polyrotaxane constructed in this way was determined by the interplay among various factors including the coordination preferences of the metal ion, spatial disposition of the donor atoms with respect to the cucurbitruil beads in the pseudorotaxane, and the size and coordination ability of the counterion. When Cu(NO3)2 was used, a one-dimensional polyrotaxane (Figure 13) was obtained.55a This polyrotaxane is important because it is the first one formed on a coordination polymer, the first one containing a cyclic component on every repeating unit, and the first one to be structurally characterized by single-crystal X-ray crystallography. Though the pseudorotaxane was used, a two-dimensional polycatenated polyrotaxane network was obtained when AgNO3 was used, while a linear one-dimensional coordination polyrotaxane was obtained when AgTos was used.55b For the pseudorotaxane in which the number of carbon atoms between the two secondary ammonium sites was five instead of four and the pyridyl groups were connected to the chain at the 3-position instead of the 4-position, a one-dimensional coordination polymer55c,f arranged in a helical fashion was generated when AgNO3 or Ag(NO3)2 was used, while a two-dimensional polyrotaxane55e with large cavities and channels was obtained when Cu(NO3)2 was used. They also prepared a three-dimensional polyrotaxane network55d from a pseudorotaxane with cyano terminal groups by using lanthanide metal ions as the linkers and square-wave-shaped one-dimensional main-chain polyrotaxanes55i from a preorganized L-shaped pseudorotaxane by using Ni2+ and Zn2+ ions as the linkers. A polypseudorotaxane was synthesized from polyviologen and cucurbituril in water by simple stirring at room temperature.55g The degree of threading (number of cucurbituril beads per repeat unit) can be precisely controlled from 0.1 to 1.0 by controlling the amount of cucurbituril added. The threaded cucurbituril beads are localized at the middle of the decamethylene units of the polymer through hydrophobic and charge-dipole interactions, to afford a well-defined microstructure in aqueous medium. Some side-chain polypseudorotaxanes containing cucurbituril were also prepared by this group.55h They exhibit higher conformational rigidity and thermal stability than their parent polymers. Furthermore, for these polypseudorotaxanes, threading and dethreading of the cucurbituril macrocycles can be reversibly controlled by the pH of the solution. Recently 26 they prepared a double-chained polyrotaxane by threading cucurbituril onto a double- chained one-dimensional coordination polymer.55j N N H2 H2 N N + + = + N N H2 H2 N N + + Cu2+ N N H2 H2 N N + + Cu L3 L = H2O n 4+ O CH2 CH2 HH O CH2 CH2 6 Cucurbituril Figure 13. Preparation of a 1 D polyrotaxane based on cucrbituril. Cucurbituril was also used in preparing polyamide-based main-chain polypseudorotaxanes and polyrotaxanes by interfacial condensation,56a,b main-chain polyrotaxanes by catalytic self-threading,56c,e and main-chain polypseudorotaxanes by post-threading.56d Chen and coworkers demonstrated the fabrication of a two-dimensional polyrotaxane network57a via π-π interactions and a three-dimensional polypseudorotaxane network57b based on metal-coordination between silver salts and flexible pyridyl-type ligands in the solid state as shown by X-ray single-crystal analysis. After the syntheses of some conducting polymers58a-d containing metallorotaxanes, Swager and coworkers58e,f reported the synthesis of the first conducting polymetallorotaxanes (Figure 14) by electrochemical polymerization of metallorotaxanes. These supra-molecular systems can reversibly bind Zn2+, Cu+, and Cu2+. Furthermore they have conductivity profiles characteristic of localized redox conductors. Later they58g used two-step electropolymerization of metallorotaxanes to prepare three-strand conducting ladder polymers, wherein one of the conjugated chains is sandwiched between two other chains. In this structure the internal polymer behaves as a partially 27 O O OOOO OOOO CH2 OH O O O O O O O O O O CH2 OH O Cl + exo esterification O O O O OOOO OOOO CH2 O O O O O O O O O O O CH2 OH O O O O O O O O O O CH2 O endo esterification 13 14 15 16 O O OOOO OOOO Figure 15. Mechanism for the formation of the mechanically branched and network polymers with a side chain rotaxane structure. Bis(polypseudorotaxane)s composed of metallobridged bis(β-cyclodextrin)s possessing the ligated copper(II) center and PEG chains were synthesized by Liu and 30 coworkers.60a An infinite mechanically linked 2D polyrotaxane network based on 1,4- bis(imidazol-1-yl-methyl)benzene was prepared by Hoskins and coworkers.60b π-π stacking and charge transfer interactions also have been used to construct polypseudorotaxanes. Owen and Hodge61 synthesized a series of polypseudorotaxanes (Figure 16) by using tetracationic cyclophane cyclobis(paraquat-phenylene) as the cyclic component. This cyclophane was quickly threaded onto some preformed polymers in acetone. High m/n values of these polypseudorotaxanes show that π-π stacking and charge transfer interactions are very efficient driving forces for the manufacture of polypseudorotaxane and polyrotaxanes. Mason and coworkers28,62a,62b,62c studied similar systems but they focused on studies of the threading process and molecular motion. Based on this tetracationic cyclophane macrocycle, Tamaoki’s group prepared a poly[2]rotaxane of type L by route IX in Scheme 1 with low molecular weight.62d PF6 - PF6 - PF6 - PF6 - = Polymer Backbone O O O O = or N N N N + ++ + Figure 16. A polypseudorotaxane with cyclobis(paraquat-phenylene) as the cyclic component Tetracationic cyclophane cyclobis(paraquat-phenylene) also was used in the preparation of polyrotaxanes for mechanical linking by a stepwise approach63a,c and polypseudorotaxanes based on conjugated polymers.63b For the later, it was found that the efficient charge transfer interaction between the electron-rich units on the conjugated polymer and the electro-poor cyclophane afforded a high conductivity of the polypseudorotaxanes. 31 Yui’s group64 also prepared a series of PEG-based hydrogels. The study of the hydrolytic erosion behavior of hydrogels cross-linked by a hydrolyzable polyrotaxane revealed that the time to reach complete gel erosion was prolonged by decreasing the polyrotaxane content and increasing the PEG/α-CD ratio.64a,b Further study was performed to evaluate their cell adhesion and proliferation.64d It was found that the cells recognize the surface heterogeneity due to the polyrotaxane structure and the cell adhesion and proliferation is controllable by the polyrotaxane content in feed. The hydrogels cross-linked by the polyrotaxane can be used as long-term stable, but actually hydrolyzable hydrogels for polymeric scaffolding in tissue engineering.64a,b Ito and coworkers65b made a polyrotaxane gel by figure of eight crosslinking. Polyrotaxane gels can be regarded as a third type of gel, separate from the chemical and physical gels because they are topological gels in which the polymer network is interlocked by topological restrictions. This group also made other polyrotaxane-related structures.65a,c Recently p-tert-butylcalix[8]arene (Figure 17) was used to construct main chain polyrotaxanes with PEG as the polymer backbone.66 These polyrotaxanes were prepared by the polycondensation of p-tert-butylphenol with paraformaldehyde in the presence of PEG. The polyrotaxane yield and the composition were dependent on the molecular weight of PEG. OH HO HO HO OH OH OH OH Figure 17. The structure of p-tert-butylcalix[8]arene 32 the exterior of the CDs, many CD-based polypseudorotaxanes and polyrotaxanes6- 9,10c,10f,47,75 are soluble in water and some polar solvents though their parent polymers are hydrophobic or nonpolar. Especially Yui’s group use this property to prepare a series of biodegradable CD-based polyrotaxanes,6-9,75d which can potentially be used as drug carriers and tissue scaffolds. The solubility of crown ether-based polypseudorotaxanes and polyrotaxanes in methanol and/or water was improved because of the hydrogen bonding between the crown ethers and solvents30,45,37a or the hydrogen bonding between the crown ethers and the polymer backbone.31b These studies imply potential applications of the polypseudorotaxane or polyrotaxane concept in coatings, adhesives, and water- borne processing.1g 1.6.2. Stability Obviously polyrotoaxanes are more thermodynamically (not necessarily thermally though) stable than their corresponding polypseudorotaxanes because of the existence of stoppers. It is also obvious that the polypseudorotaxanes/polyrotaxanes with attractive forces, such as hydrogen bonding and charge transfer, between their components are more stable that those without attractive forces between their components. This is the reason that few polypseudorotaxanes and polyrotaxanes were prepared in recent years by statistical threading and chemical conversion.1g Though there are strong attractive forces between their components, dethreading still can happen in some polypseudorotaxane, and polyrotaxane systems when a salt or other substance is added or the temperature increases.1g Recently Yui and coworkers10c,f found the thermal stability of their biodegradable polyrotaxane is better than the thermal stability of the separate components, poly(ε-lysine) and α-cyclodextrin. They thought this was because of the formation of complex. The same results were obtained in the studies of polypseudorotaxanes based on α-CD and PPG-PEG-PPG triblock copolymers15g and polypseudorotaxanes of α- and γ- CDs with poly(butylenes carbonate).76 35 1.6.3. Photoelectronic properties The introduction of photo- and electronic-active elements into the polypseudorotaxane and polyrotaxane structure has led to the studies of the photoelectronic properties of these materials. A [2]rotaxane77 was synthesized from a Zn(II)-phthalocyanine with polyether substituents containing π electron rich hydroquinone segments and a cyclobis(paraquat-p- phenylene) tetracation containing π electron deficient bipyridinium units. It was found that fluorescence quenching of the Zn(II)-phthalocyanine was enhanced dramatically in MeCN. Swager and coworkers51 observed the same phenomenon in their polyrotaxane systems. It was believed that this phenomenon was caused by rapid migration of the hole- electron pair to the rotaxane sites followed by rapid combination. They also found that the conductivity of these polyrotaxanes was lower than the parent polymer. Some conjugated polyrotaxanes containing metals were synthesized by Sauvage’s group.59,78 The deposition of electroactive films with a polyrotaxane organic backbone using a pre-assembling principle was described.78a These films can retain their structure and the metal can be reintroduced after demetallation. Later they made some conducting polyrotaxanes.59,78c It was found that the Cu(I) binding was reversible only if lithium was present during copper removal. A series of polyrotaxanes as a light-harvesting antenna model was constructed by Ueno and coworkers.79 These polyrotaxanes consists of various ratios of α-CD and naphthalene-appended α-CD threaded by a PEG chain bearing anthracene moieties at each end. Here naphthalene and anthracene moieties act as energy donors and energy acceptors, respectively. It was found that antenna effect becomes more marked with increasing number of naphthalene-appended α-CD units in the polyrotaxanes, but energy transfer efficiency decrease with this increase. 1.6.4. Viscosity The threading of cyclic components onto the polymer backbone has an important influence on the solution viscosity and melt viscosity. Up to now it has been found that 36 this influence depends on the properties of cyclic components and the polymer backbone, the value of m/n, and the types of solvents. Gibson and coworkers38b studied the effect of the threading on the solution viscosity of polypseudorotaxanes. It was found that the higher the degree of threading, m/n, the higher the intrinsic viscosity. Several factors were believed to have attributed to this increase. Upon threading, the solvated volume of the polymer will increase and lead to the higher viscosity. The chain extension resulting from the ionic repulsion between the complexed dicationic paraquat guests can also increase the viscosity. Furthermore, as the degree of threading increases, these repulsive forces will also be more prevalent. This effect can also cause the viscosity to increase. This group30,80 also found that poly(ester rotaxane)s have higher intrinsic viscosities than their parent polymers because of the increase of hydrodynamic volume due to the presence of the cyclic components. The types of solvents could also affect the viscosity of polyrotaxanes.30 When the solvent was changed from THF to a mixture of THF and methanol (10:1), the intrinsic viscosity of polyrotaxane decreased, while the intrinsic viscosities of the parent homopolymer and a copolymer with poly(ethylene oxide) were unaffected by the solvent change. This solvent dependence is due to the differential solvation of the linear and cyclic components. In the studies of poly(urethane-crown ether rotaxane),81 it was also found that the polyrotaxane had higher viscosity than the corresponding parent polyurethane because the presence of the cyclic species causes the polyrotaxane adopt an expanded conformation. Wenz and Keller4a observed that the viscosity of their CD-based main- chain poly(amine rotaxane) increased with increasing m/n. Even for side-chain poly(methacrylate CD rotaxane)s,47 viscosities were higher than those of the model systems. Though the solution viscosities of polypseudorotaxanes and polyrotaxane are higher than their parent polymers, the melt viscosity of a poly(ester rotaxane) studied by Gibson’s group was lower than that of the corresponding model polymer.30,80 This is because the cyclic components prevent polymer chain entanglements in the melt state, and therefore the melt viscosity decreases. 37 1.7. CONCLUSIONS AND PERSPECTIVE Because of the introduction of mechanical linking, polypseudorotaxanes and polyrotaxanes have novel topologies and properties compared with conventional small molecules and polymers. These supramolecular materials are studied all over the world now. Depending on how the cyclic and linear components are connected, polypseudorotaxanes and polyrotaxanes can be divided into main-chain, side chain, and others. The most commonly used macrocycles for the construction of polypseudorotaxanes and polyrotaxanes are crown ethers and cyclodextrins though other macrocycles, such as cucurbituril and tetracationic bisparaquat cyclophane, are also used. A lot of tools have been employed to characterize polypseudorotaxanes and polyrotaxanes. However, the most powerful tool is NMR. Due to their novel topologies, polypseudorotaxanes and polyrotaxanes have different properties, including solubility, stability, photoelectronic properties, viscosity, phase behavior, from conventional polymers. Studies have demonstrated that the degree of to which they differ depends on not only the properties of threaded cyclic and linear components but also the threading efficiency. From previous analysis, we know that low association constants have limited the preparation of large supramolecular systems. It also has an important influence on the stability of supramolecular systems. The requirement for high association constants makes it necessary to prepare new more powerful hosts and guests. Most of the polypseudorotaxanes and polyrotaxanes obtained up to now are linear. The possibility of making two and three dimensional polypseudorotaxanes and polyrotaxanes, such as hyperbranched, dendritic, and crosslinked ones (Figure 18), is very interesting and important in terms of new topologies and properties. Molecular weight and polydispersity are two important factors determining the ultimate properties of polymers. Using recently developed living polymerization methods,88 such as SFRP89 (stable free radical polymerization), and the feature of mechanical linking of pseudorotaxanes and rotaxanes, we can prepare non-covalent (mechanical) reversible block and graft copolymers with 40 pseudorotaxane structure (Figure 19) with precisely controlled molecular weight and polydispersity. Furthermore, if stoppers are introduced in these copolymers, they will change into non-covalent copolymers with rotaxane-type mechanically interlocked structures. This is one advantage compared with non-covalent copolymers employing the non-threaded structures based on H-bonding or other non-covalent interactions.90 n Crosslinked Polyrotaxane n Hyperbranched Polyrotaxane Hyperbranched Polypseudorotaxane Dendritic Polypseudorotaxane Dendritic Polyrotaxane Crosslinked Polypseudorotaxane Figure 18. Polypseudorotaxanes and polyrotaxanes with new topologies. 41 AB non-covalent diblock copolymer ABA non-covalent triblock copolymer BAB non-covalent triblock copolymer Polymer A Polymer B n n non-covalent graft copolymers n (a) (b) (c) Figure 19. Non-covalent block and graft copolymers with pseudorotaxane structures. Acknowledgements This work was supported by the National Science Foundation (DMR0097126) and the Petroleum Research Fund (40223-AC7). 42 3775-3777. (f) Choi, H. S.; Huh, K. M.; Ooya, T.; Yui, N. pH- and thermosensitive supramolecular assembling system: rapidly responsive properties of β-cyclodextrin- conjugated poly(ε-lysine). J. Am. Chem. Soc. 2003, 125, 6350-6351. (g) Choi, H. S.; Ooya, T.; Sasaki, S.; Yui, N.; Ohya, Y.; Nakai, T.; Ouchi, T. Preparation and characterization of polypseudorotaxanes based on biodegradable poly(L- lactide)/poly(ethylene glycol) triblock copolymers. Macromolecules 2003, 36, 9313-9318. (h) Choi, H. S.; Ooya, T.; Lee, S. C.; Sasaki, S.; Kurisawa, M. Uyama, H.; Yui, N. pH dependence of polypseudorotaxane formation between cationic linear polyethylenimine and cyclodextrins. Macromolecules 2004, 37, 6705-6710. (i) Lee, S. C.; Choi, H. S.; Ooya, T.; Yui, N. Block-selective polypseudorotaxane formation in PEI-b-PEG-b-PEI copolymers via pH variation. Macromolecules 2004, 37, 7464-7468. 11. Ooya. T.; Eguchi, M.; Yui, N. Enhanced accessibility of peptide substrate toward membrane-bound metalloexopeptidase by supramolecular structure of polyrotaxane. Biomacromolecules 2001, 2, 200-203. 12. Ooya, T.; Yui, N. Synthesis of theophylline-polyrotaxane conjugates and their drug release via supramolecular dissociation. J. Controlled Release 1999, 58, 251-269. Ooya, T.; Arizono, K.; Yui, N. Synthesis and characterization of an oligopeptide- terminated polyrotaxane as a drug carrier. Polym. Adv. Technol. 2000, 11, 642-651. Park, H. D.; Lee, W. K.; Ooya, T.; Park, K. D.; Kim, Y. H.; Yui, N. Anticoagulant activity of sulfonated polyrotaxanes as blood-compatible materials. J. Biomed. Mater. Res. 2002, 60, 186-190. Yui, N.; Ooya, T.; Kawashima, T.; Saito, Y.; Tamai, I.; Sai, Y.; Tsuji, A. Inhibitory effect of supramolecular polyrotaxane- dipeptide conjugates on digested peptide uptake via intestinal human peptide transporter. Bioconjugate Chem. 2002, 13, 582-587. Huh, K. M.; Tomita, H.; Lee, W. K.; Ooya, T.; Yui, N. Synthesis of α-cyclodextrin-conjugated poly(ε-lysine)s and their inclusion complexation behavior. Macromol. Rapid Commun. 2002, 23, 179-182. Ooya, T.; Yui, N. Multivalent interactions between biotin-polyrotaxane conjugates and streptavidin as a model of new targeting for transporters. J. Controlled Release 2002, 80, 219-228. Lee, W. K.; Kobayashi, J.; Ooya, T.; Park, K. D.; Yui, N. Synthesis and characterization of nitric oxide generative 45 polyrotaxane. J. Biomater. Sci. Polym. Ed. 2002, 13, 1153-1161. Eguchi, M.; Ooya, T.; Yui, N. Controlling the mechanism of trypsin inhibition by the numbers of α- cyclodextrins and carboxyl groups in carboxyethylester-polyrotaxanes. J. Controlled Release 2004, 96, 301-307. Ooya, T.; Yamashita, A.; Kurisawa, M.; Sugaya, Y.; Maruyama, A.; Yui, N. Effects of polyrotaxane structure on polyion complexation with DNA. Sci Technol Adv. Mater. 2004, 5, 363-369. Ooya, T.; Yui, N. Synthesis of theophylline-polyrotaxane conjugates and their drug release via supramolecular dissociation. J. Controlled Release 1999, 58, 251-269. 13. Sano, H.; Ichi, T.; Kumashiro, Y.; Kontani, K.; Kuze, T.; Mizutani, G.; Ooya, T.; Yui, N. Raman scattering study of water clusters around polyrotaxane and pseudopolyrotaxane supramolecular assemblies. Spectrochim. Acta A 2003, 59, 285-289. Hiroaki, H.; Sano, H.; Mizutani, G.; Eguchi, M.; Ooya, T.; Yui, N. Effect of the mobility of ligands in polyrotaxanes on order structure of water clusters. Langmuir 2004, 20, 2852-2854. 14. (a) Ooya, T.; Eguchi, M.; Yui, N. Supramolecular design for multivalent interaction: maltose mobility along polyrotaxane enhanced binding with concanavalin A. J. Am. Chem. Soc. 2003, 125, 13016-13017. (b) Nelson, A.; Stoddart, J. F. Dynamic multivalent lactosides displayed on cyclodextrin beads dangling from polymer strings. Org. Lett. 2003, 5, 3783-3786. (c) Nelson, A.; Belitsky, J. M.; Vidal, S.; Joiner, C. S.; Baum, L. G.; Stoddart, J. F. A self- assembled multivalent pseudopolyrotaxane for binding galectin-1. J. Am. Chem. Soc. 2004, 126, 11914-11922. 15. (a) Ceccato, M.; Lo Nostro, P.; Baglioni, P. α-Cyclodextrin/polyethylene glycol polyrotaxane: a study of the threading process. Langmuir 1997, 13, 2436-2439. (b) Lo Nostro, P.; Lopes, J. R.; Cradelli, C. Formation of cyclodextrin-based polypseudorotaxanes: solvent effect and kinetic study. Langmuir 2001, 17, 4610- 4615. (c) Li, J.; Li, X.; Toh, K. C.; Ni, X.; Zhou, Z.; Leong, K. W. Inclusion complexation and formation of polypseudorotaxanes between poly[(ethylene oxide)-ran-(propylene oxide)] and cyclodextrins. Macromolecules 2001, 34, 8829- 8831. (d) Lo Nostro, P.; Lopes, J. R.; Ninham, B. W.; Baglioni, P. Effect of cations and anions on the formation of polypseudorotaxanes. J. Phys. Chem. B 2002, 106, 46 2166-2174. (e) Tait, C. N.; Davies, D. M. Polypseudorotaxanes from scratch. Langmuir 2002, 18, 2453-2454. (f) Becheri, A.; Lo Nostro, P.; Ninham, B. W.; Baglioni, P. The curious world of polypseudorotaxanes: cyclodextrins as probes of water structure. J. Phys. Chem. B 2003, 107, 3979-3987. (g) Li, J.; Ni, X.; Zhou, Z.; Leong, K. W. Preparation and characterization of polypseudorotaxanes based on block-selected inclusion complexation between poly(propylene oxide)- poly(ethylene oxide)-poly(propylene oxide) triblock copolymers and α- cyclodextrin. J. Am. Chem. Soc. 2003, 125, 1788-1795. 16. Harada, A.; Li, J.; Kamachi, M. Synthesis of a tubular polymer from threaded cyclodextrins. Nature 1993, 364, 516-518. 17. (a) Ikeda, T.; Ooya, T.; Yui, N. Inclusion complexation of fractionated α- cyclodextrin molecular tube with sodium dodecyl sulfate. Polym. Adv. Technol. 2000, 11, 830-836. (b) Ikeda, T.; Ooya, T.; Yui, N. Supramolecular network formation through inclusion complexation of an α-cyclodextrin-based molecular tube. Macromol. Rapid. Commun. 2000, 21, 1257-1262. (c) Ikeda, T.; Hirota, E.; Ooya, T.; Yui, N. Thermodynamic analysis of inclusion complexation between α- cyclodextrin-based molecular tube and sodium alkyl sulfonate. Langmuir 2001, 17, 234-238. (d) Ikeda, T.; Lee, W. K.; Ooya, T.; Yui, N. Thermodynamic analysis of inclusion complexation between α-cyclodextrin-based molecular tube and poly(ethylene oxide)-block-poly(tetrahydrofuran)-block-poly(ethylene oxide) triblock copolymer. J. Phys. Chem. B 2003, 107, 14-19. 18. (a) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.; Nakashima, N. A light-driven molecular shuttle based on a rotaxane. J. Am. Chem. Soc. 1997, 119, 7605-7606. (b) Harada, A. Polyrotaxanes. Acta Polym. 1998, 49, 3-17. 19. (a) Yamaguchi, I.; Takenaka, Y.; Osakada, K.; Yamamoto, T. Preparation and characterization of polyurethane-cyclodextrin pseudopolyrotaxanes. Macromolecules 1999, 32, 2051-2054. (b) Yamaguchi, I.; Osakada, K.; Yamamoto, T. Pseudopolyrotaxane composed of an azobenzene polymer and γ-cyclodextrin. reversible and irreversible photoisomerization of the azobenzene groups in the polymer chain. Chem. Commun. 2000, 1335-1336. (c) Yamaguchi, I.; Miya, K.; 47 125, 14458-14464. Huang, F.; Fronczek, F. R.; Gibson, H. W. First supramolecular poly(taco complex). Chem. Commun. 2003, 1480-1481. 29. (a) Wu, C.; Bheda, M. C.; Lim, C.; Shen, Y. X.; Sze, J. Y.; Gibson, H. W. Synthesis of polyester rotaxanes via the statistical threading method. Polym. Commun. 1991, 32, 204-207. (b) Gibson, H. W.; Liu, S.; Lecavalier, P.; Wu, C.; Shen, Y. X. Synthesis and preliminary characterization of some polyester rotaxanes. J. Am. Chem. Soc. 1995, 117, 852-874. 30. Gibson, H. W.; Liu, S.; Gong, C.; Ji, Q.; Joseph, E. Studies of the Formation of Poly(ester rotaxane)s from Diacid Chlorides, Diols, and Crown Ethers and Their Properties. Macromolecules 1997, 30, 3711-3727. 31. (a) Shen, Y. X.; Gibson, H. W. Synthesis and some properties of polyrotaxanes comprised of polyurethane backbone and crown ethers. Macromolecules 1992, 25, 2058-2059. (b) Shen, Y. X.; Xie, D.; Gibson, H. W. Polyrotaxanes based on polyurethane backbones and crown ether cyclics. 1. synthesis. J. Am. Chem. Soc. 1994, 116, 537-548. (c) Loveday. D.; Wilkes, G. L.; Bheda, M. C.; Shen, Y. X. Structure-property relationships in segmented polyviologen ionene rotaxanes. Gibson, H. W. J. Macromol. Sci. A-Chem. 1995, A32, 1-27. 32. (a) Marand, E.; Hu, Q.; Gibson, H. W.; Veystman, B. Spectroscopic characterization of hydrogen bonding in poly(urethane-rotaxane)s. Macromolecules 1996, 29, 2555-2562. (b) Gong, C.; Gibson, H. W. Controlling microstructure in polymeric molecular shuttles: solvent-induced localization of macrocycles in poly(urethane/crown ether) rotaxanes. Angew. Chem. Int. Ed. Engl. 1997, 36, 2331- 2333. 33. (a) Gong, C.; Gibson, H. W. Synthesis and characterization of a polyester/crown ether rotaxane derived from a difunctional blocking group. Macromolecules 1996, 29, 7029-7033. (b) Gong, C.; Gibson, H. W. Dethreading during the preparation of polyrotaxanes. Macromol. Chem. Phys. 1997, 198, 2321-2332. (c) Gong, C.; Ji, Q.; Glass, T. E.; Gibson, H. W. A strategy to eliminate dethreading during the preparation of poly(ester/crown ether rotaxane)s: use of difunctional blocking groups. Macromolecules 1997, 30, 4807-4813. 34. Gong, C.; Gibson, H. W. Relative threading efficiencies of different macrocycles: a 50 competitive trapping methodology based on hybrid polyrotaxanes. Macromolecules 1997, 30, 8524-8525. 35. Gong, C.; Glass, T. E.; Gibson, H. W. Poly(urethane/crown ether rotaxane)s with solvent switchable microstructures. Macromolecules 1998, 31, 308-313. 36. (a) Lee, S. H.; Engen, P. T.; Gibson, H. W. Blocking group/initiators for the synthesis of polyrotaxanes via free radical polymerizations. Macromolecules 1997, 30, 337-343. (b) Gibson, H. W.; Engen, P. T.; Lee, S.-H. Synthesis of poly[(styrene)-rotaxa-(crown ether)]s via free radical polymerization. Polymer 1999, 40, 1823-1832. 37. (a) Gibson, H. W.; Engen, P. T. Rotaxanes based on polyacrylonitrile. New J. Chem. 1993, 17, 723-727. (b) Nagapudi, K.; Leisen, J.; Beckham, H. W.; Gibson, H. W. Solid-state NMR investigations of poly[(acrylonitrile)-rotaxa-(60-crown- 20)]. Macromolecules 1999, 32, 3025-3033. 38. (a) Gong, C.; Gibson, H. W. Self-assembly of novel polyrotaxanes: main-chain pseudopolyrotaxanes with poly(ester crown ether) backbones. Angew. Chem. Int. Ed. Engl. 1998, 37, 310-314. (b) Gong, C.; Balanda, P. B.; Gibson, H. W. Supramolecular chemistry with macromolecules: new self-assembly based main chain polypseudorotaxanes and their properties. Macromolecules 1998, 31, 5278- 5289. 39. Gong, C.; Gibson, H. W. Self-threading-based approach for branched and/or cross- linked poly(methacrylate rotaxane)s. J. Am. Chem. Soc. 1997, 119, 5862-5866. 40. Gibson, H. W.; Nagvekar, D.; Powell, J.; Gong, C.; Bryant, W. S. Polyrotaxanes by in situ self threading during polymerization of functional macrocycles. Part 2. Poly(ester crown ether)s. Tetrahedron 1997, 53, 15197-15207. 41. Gong, C.; Gibson, H. W. Controlling polymeric topology by polymerization conditions: mechanically linked network and branched poly(urethane rotaxane)s with controllable polydispersity. J. Am. Chem. Soc. 1997, 119, 8585-8591. 42. (a) Delaviz, Y.; Gibson, H. W. Macrocyclic polymers. 2. Synthesis of poly(amide crown ethers) based on bis(5-carboxy-1,3-phenylene)-32-crown-10. Network formation through threading. Macromolecules 1992, 25, 4859-4862. (b) Gibson, H. W.; Nagvekar, D. S.; Yamaguchi, N.; Bhattacharjee, S.; Wang, H.; Vergne, M. J.; 51 Hercules, D. M. Polyamide pseudorotaxanes, rotaxanes, and catenanes based on bis(5-carboxy-1,3-phenylene)-(3x+2)-crown-x ethers. Macromolecules 2004, 37, 7514-7529. 43. Gong, C.; Ji, Q.; Subramaniam, C.; Gibson, H. W. Main chain polyrotaxanes by threading crown ethers onto a preformed polyurethane: preparation and properties. Macromolecules 1998, 31, 1814-1818. 44. Gong, C.; Gibson, H. W. Polyrotaxanes and related structures: synthesis and properties. Curr. Opin. Solid. State. Mater. Sci. 1997, 2, 647-652. 45. Gibson, H. W.; Liu, S. Polyrotaxanes: past, present and future. Macromol. Symp. 1996, 102, 55-61. 46. Nagapudi, K.; Hunt, J.; Shepherd, C.; Baker, J.; Beckham, H. W. Synthesis, dynamic mechanical, and solid-state NMR spectroscopy of crown-ether-based linear aliphatic polyurethane rotaxanes. Macromol. Chem. Phys. 1999, 200, 2541- 2550. 47. Born, M.; Ritter, H. Comb-like rotaxane polymers containing non-covalently bound cyclodextrins in the side chains. Makromol. Chem. Rapid Commun. 1991, 12, 471- 476. 48. Born, M.; Ritter, H. Topologically unique side-chain polyrotaxanes based on triacetyl-β-cyclodextrin and a poly(ether sulfone) main chain. Macromol. Rapid Commun. 1996, 17, 197-202. 49. (a) Born, M.; Ritter, H. Pseudo-polymer analogous reactions. Methylation of alcohol groups of noncovalently anchored 2,6-dimethyl-β-cyclodextrin components located in branched side chains of a poly(tandem-rotaxane). Adv. Mater. 1996, 8, 149-151. (b) Noll, O.; Ritter, H. New side chain poly(methacryl-rotaxanes) bearing cyclodextrins as non-covalently anchored ring components. Chemoenzymic synthesis and degradation. Macromol. Rapid Commun. 1997, 18, 53-58. (c) Noll, O.; Ritter, H. Synthesis of new side-chain polyrotaxanes via free radical polymerization of a water-soluble semi-rotaxane monomer consisting of 2,6- dimethyl-β-cyclodextrin and 3-O-(11-acryloylaminoundecanoyl)cholic acid. Macromol. Chem. Phys. 1998, 199, 791-794. 50. Yamaguchi, I.; Osakada, K.; Yamamoto, T. A novel crown ether stopping group for 52 and flexible pyridyl-type ligands. Inorg. Chem. 2002, 41, 4846-4848. 58. (a) Dietrich-Buchecker, C.; Sauvage, J. P. Template synthesis of interlocked macrocyclic ligands, the catenands. Preparation and characterization of the prototypical bis-30 membered ring system. Tetrahedron 1990, 46, 503-512. (b) Sauvage, J. P. Interlacing molecular threads on transition metals: catenands, catenates, and knots. Acc. Chem. Res. 1990, 23, 319-327. (c) Arrnaroli, N.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L.; Sauvage, J. P.; Hemmert, C. J. Am. Chem. Soc. 1994, 116, 5211-5217. (d) Sleiman, H.; Baxter, P.; Lehn, J.-M.; Rissanen, K. J. Chem. Soc. Chem. Commun. 1995, 715-716. (e) Zhu, S. S.; Carroll, P. J.; Swager, T. M. Conducting polymetallorotaxanes: a supramolecular approach to transition metal ion sensors. J. Am. Chem. Soc. 1996, 118, 8713-8714. (f) Zhu, S. S.; Swager, T. M. Conducting polymetallorotaxanes: metal ion mediated enhancements in conductivity and charge localization. J. Am. Chem. Soc. 1997, 119, 12568-12577. (g) Buey, J.; Swager, T. M. Three-strand conducting ladder polymers: two-step electropolymerization of metallorotaxanes. Angew. Chem. Int. Ed. 2000, 39, 608-612. 59. (a) Vidal, P. L.; Billon, M.; Divisia-Blohorn, B.; Bidan, G.; Kern, J.-M.; Sauvage, J.-P. Conjugated polyrotaxanes containing coordinating units: reversible copper(I) metallation-demetallation using lithium as intermediate scaffolding. Chem. Commun. 1998, 629-630. (b) Vidal, P. L.; Divisia-Blohorn, B.; Bidan, G.; Kern, J. M.; Sauvage, J. P.; Hazemann, J. L. Conjugated polyrotaxanes incorporating mono- or mivalent copper complexes. Inorg. Chem. 1999, 38, 4203-4210. (c) Sauvage, J.- P.; Kern, J.-M.; Bidan, G.; Divisia-Blohorn, B.; Vidal, P. Conjugated polyrotaxanes: improvement of the polymer properties by using sterically hindered coordinating units. New J. Chem. 2002, 26, 1287-1290. Divisia-Blohorn, B.; Genoud, F.; Borel, C.; Bidan, G.; Kern, J.-M.; Sauvage, J.-P. Conjugated polymetallorotaxanes: in-situ ESR and conductivity investigations of metal- backbone interactions. J. Phys. Chem. B 2003, 107, 5126-5132. 60. (a) Hoskins, B. F.; Robson, R.; Silzys, D. A. An infinite 2D polyrotaxane network in Ag2(bix)3(NO3)2 (bix = 1,4-bis(imidazol-1-ylmethyl)benzene). J. Am. Chem. Soc. 1997, 119, 2952-2953. (b) Liu, Y.; Li, L.; Zhang, H.-Y.; Zhao, Y.-L.; Wu, X. 55 Bis(pseudopolyrotaxane)s possessing copper(II) ions formed by different polymer chains and bis(β-cyclodextrin)s bridged with a 2,2'-bipyridine-4,4'-dicarboxy tether. Macromolecules 2002, 35, 9934-9938. 61. Owen, G. J.; Hodge, P. Synthesis of some new polypseudorotaxanes. Chem. Commun. 1997, 11-12. Hodge, P.; Monvisade, P.; Owen, G. J.; Heatley, F.; Pang, Y. 1H NMR spectroscopic studies of the structures of a series of pseudopolyrotaxanes formed by "threading". New J. Chem. 2000, 24, 703-709. 62. (a) Mason, P. E.; Parsons, I. W.; Tolley, M. S. The first demonstration of molecular queuing in pseudo[η]polyrotaxanes: a novel variant of supramolecular motion. Angew. Chem. Int. Ed. Engl. 1996, 35, 2238-2241. (b) Mason, P. E.; Parsons, I. W.; Tolley, M. S. Dynamic behavior of a pseudo[n]polyrotaxane containing a bipyridyl- based cyclophane: spectroscopic observations. Polymer 1998, 39, 3981-3991. (c) Mason, P. E.; Bryant, W. S.; Gibson, H. W. Threading/dethreading exchange rates as structural probes in polypseudorotaxanes. Macromolecules 1999, 32, 1559-1569. (d) Belaissaoui, A.; Shimada, S.; Ohishi, A.; Tamaoki, N. Synthesis of a mechanically linked oligo[2]rotaxane. Tetrahedron Lett. 2003, 44, 2307-2310. 63. (a) Werts, M. P. L.; van den Boogaard, M.; Hadziioannou, G.; Tsivgoulis, G. M. Towards mechanically linked polyrotaxanes by sequential deprotection-coupling steps of bifunctional rotaxanes. Chem. Commun. 1999, 623-624. (b) Naka K, Uemura T, Chujo Y. Self-complexation of a poly-conjugated donor molecule with a cyclic acceptor. Bull. Chem. Soc. Jpn. 2002, 75, 2053-2057. (c) Werts, M. P. L.; van den Boogaard, M.; Tsivgoulis, G. M.; Hadziioannou, G. Mechanically linked polyrotaxanes: a stepwise approach. Macromolecules 2003, 36, 7004-7013. 64. (a) Watanabe, J.; Ooya, T.; Park, K. D.; Kim, Y. H.; Yui, N. Preparation and characterization of poly(ethylene glycol) hydrogels crosslinked by hydrolyzable polyrotaxane. J. Biomater. Sci., Polym. Ed. 2000, 11, 1333-1345. (b) Ichi, T.; Watanabe, J.; Ooya, T.; Yui, N. Controllable Erosion Time and Profile in Poly(ethylene glycol) Hydrogels by Supramolecular Structure of Hydrolyzable Polyrotaxane. Biomacromolecules 2001, 2, 204-210. (c) Huh, K. M.; Ooya, T.; Lee, W. K.; Sasaki, S.; Kwon, I. C.; Jeong, S. Y.; Yui, N. Supramolecular-structured hydrogels showing a reversible phase transition by inclusion complexation between 56 poly(ethylene glycol) grafted dextran and α-cyclodextrin. Macromolecules 2001, 34, 8657-8662. (d) Watanabe, J.; Ooya, T.; Nitta, K.-H.; Park, K. D.; Kim, Y. H.; Yui, N. Fibroblast adhesion and proliferation on poly(ethylene glycol) hydrogels crosslinked by hydrolyzable polyrotaxane. Biomaterials 2002, 23, 4041-4048. (e) Choi, H. S.; Kontani, K.; Huh, K. M.; Sasaki, S.; Ooya, T.; Lee, W. K.; Yui, N. Rapid induction of thermoreversible hydrogel formation based on poly(propylene glycol)-grafted dextran inclusion complexes. Macromol. Biosci. 2002, 2, 298-303. (f) Ichi, T.; Ooya, T.; Yui, N. Supramolecular control of ester hydrolysis in poly(ethylene glycol)-interlocked hydrogels. Macromol. Biosci. 2003, 3, 373-380. (g) Ooya, T.; Kobayashi, N.; Ichi, T.; Sasaki, S.; Yui, N. Hydrogels having tubular α-cyclodextrin structure: effect of nano-tube structure on long alkyl chain partitions. Sci. Technol. Adv. Mater. 2003, 4, 39-42. (h) Ichi, T.; Nitta, K.; Lee, W. K.; Ooya, T.; Yui, N. Preparation of porous hydrolyzable polyrotaxane hydrogels and their erosion behavior. J. Biomater. Sci. Polym. Ed. 2003, 14, 567-579. (i) Huh, K. M.; Cho, Y. W.; Chung, H.; Kwon, I. C.; Jeong, S. Y.; Ooya, T.; Lee, W. K.; Sasaki, S.; Yui, N. Supramolecular hydrogel formation based on inclusion complexation between poly(ethylene glycol)-modified chitosan and α-cyclodextrin. Macromol. Biosci. 2004, 4, 92-99. (j) Tachaboonyakiat, W.; Furubayashi, T.; Katoh, M.; Ooya, T.; Yui, N. Novel biodegradable cholesterol-modified polyrotaxane hydrogels for cartilage regeneration. J. Biomater. Sci. Polym. Ed. 2004, 15, 1389-1404. 65. (a) Ikeda, E.; Okumura, Y.; Shimomura, T.; Ito, K.; Hayakawa, R. Inclusion behavior between molecular nanotubes and linear polymer chains in aqueous solutions. J. Chem. Phys. 2000, 112, 4321-4325. (b) Okumura, Y.; Ito, K. The polyrotaxane gel: a topological gel by figure-of-eight cross-links. Adv. Mater. 2001, 13, 485-487. (c) Karino, T.; Okumura, Y.; Ito, K.; Shibayama, M. SANS studies on spatial inhomogeneities of slide-ring gels. Macromolecules 2004, 37, 6177-6182. 66. Yamagishi, T.-A.; Kawahara, A.; Kita, J.; Hoshima, M.; Umehara, A.; Ishida, S.; Nakamoto, Y. In situ polycondensation of p-tert-butylphenol in the presence of poly(ethylene glycol)s for preparation of polyrotaxanes. Macromolecules 2001, 34, 6565-6570. 57 Chem. Soc., Perkin. Trans. 2. 2001, 2012-2021. Tamura, M.; Gao, D.; Ueno, A. A polyrotaxane series containing alpha-cyclodextrin and naphthalene-modified alpha- cyclodextrin as a light-harvesting antenna system. Chemistry 2001, 7, 1390-1397. Tamura, M.; Gao, D.; Ueno, A. A polyrotaxane series containing α-cyclodextrin and naphthalene-modified α-cyclodextrin as a light-harvesting antenna system. Chem. Eur. J. 2001, 7, 1390-1397. 80. Gibson, H. W.; Gong, C.; Liu, S.; Nagvekar, D. S. New polymer architectures. recent results with polyrotaxanes. Macromol. Symp. 1998, 128, 89-98. 81. Shen, Y. X.; Lim, C.; Gibson, H. W. Synthesis of polyurethane-based polyrotaxanes. Am. Chem. Soc., Div. Polym. Chem. 1991, 32, 166-167. 82. Han, B.-H.; Antonietti, M. Cyclodextrin-based pseudopolyrotaxanes as templates for the generation of porous silica materials. Chem. Mater. 2002, 14, 3477-3485. 83. Han, B.-H.; Smarsly, B.; Gruber, C.; Wenz, G. Towards porous silica materials via nanocasting of stable pseudopolyrotaxanes from α-cyclodextrin and polyamines. Microporous Mesoporous Mater. 2003, 66, 127-132. 84. Ooya. T.; Eguchi, M.; Ozaki, A.; Yui, N. Carboxyethyl ester-polyrotaxanes as a new calcium chelating polymer: synthesis, calcium binding and mechanism of trypsin inhibition. Int. J. Pharm. 2002, 242, 47-54. 85. (a) Zhao, T. Beckham, H. W.; Gibson, H. W. Quantitative determination of threading in rotaxanated polymers by diffusion-ordered NMR spectroscopy. Macromolecules 2003, 36, 4833-4837. (b) Zhao, T.; Beckham, H. W. Direct synthesis of cyclodextrin-rotaxanated poly(ethylene glycol)s and their self-diffusion behavior in dilute solution. Macromolecules 2003, 36, 9859-9865. 86. Singla, S.; Zhao, T.; Beckham, H. W. Purification of cyclic polymers prepared from linear precursors by inclusion complexation of linear byproducts with cyclodextrins. Macromolecules 2003, 36, 6945-6948. 87. Ogoshi, T.; Chujo, Y. Synthesis of organic-inorganic polymer hybrids by means of host-guest interaction utilizing cyclodextrin. Macromolecules 2003, 36, 654-660. 88. A recent review about living polymerization: Hawker, C. J.; Bosman, A. W.; Harth, E. New polymer synthesis by nitroxide mediated living radical polymerizations. Chem. Rev. 2001, 123, 11327-11328. 60 89. Some recently published papers about the applications of SFRP in the preparation of block and graft copolymers: Meyer, U.; Svec, F.; Fréchet, J. M. J.; Hawker, C. J.; Irgum, K. Use of stable free radicals for the sequential preparation and surface grafting of functionalized macroporous monoliths. Macromolecules 2000, 33, 7769-7775. Harth, E.; Hawker, C. J.; Fan, W.; Waymouth, R. M. Chain end functionalization in nitroxide-mediated "living" free radical polymerizations. Macromolecules 2001, 34, 3856-3862. Viklund C, Nordstroem A, Irgum K, Svec F, Fréchet JMJ. Preparation of porous poly(styrene-co-divinylbenzene) monoliths with controlled pore size distributions initiated by stable free radicals and their pore surface functionalization by grafting. Macromolecules 2001, 34, 4361-4369. Knoop, C. A.; Studer, A. Hydroxy- and silyloxy-substituted TEMPO derivatives for the living free-radical polymerization of styrene and n-butyl acrylate: synthesis, kinetics, and mechanistic studies. J. Am. Chem. Soc. 2003, 125, 16327-16333. Szkurhan, A. R.; Georges, M. K. Stable free-radical emulsion polymerization. Macromolecules 2004, 37, 4776-4782. 90. Söntjens, S. H. M.; Sijbesma, R. P.; van Genderen, M. H. P.; Meijer, E. W. Selective formation of cyclic dimers in solutions of reversible supramolecular polymers. Macromolecules 2001, 34, 3815-3818. ten Cate, A. T.; Kooijman, H.; Spek, A. L.; Sijbesma, R. P.; Meijer, E. W. Conformational control in the cyclization of hydrogen-bonded supramolecular polymers. J. Am. Chem. Soc. 2004, 126, 3801-3808. Heng, X.; Rudkevich, D. M. CO2 in supramolecular chemistry: Preparation of switchable supramolecular polymers. Chem. Eur. J. 2004, 10, 5432- 5442. Heng, X.; Rudkevich, D. M. Reversible chemistry of CO2 in the preparation of fluorescent supramolecular polymers. J. Org. Chem. 2004, 69, 8609-8617. Hofmeier, H.; El-ghayoury, A.; Schenning, A. P. H. J.; Schubert, U. S. New supramolecular polymers containing both terpyridine metal complexes and quadruple hydrogen bonding units. Chem. Commun. 2004, 3, 318-319. 61