Macromolecular [2]rotaxanes comprising a polymer axle and crown ether wheel were synthesized to evaluate the effect of component mobility on the properties of the axle polymer, especially its crystallinity. Living ring-opening polymerization of δ-valerolactone with a pseudorotaxane initiator with a hydroxy group at the axle terminus was followed by end-capping with a bulky isocyanate. This yielded macromolecular [2]rotaxanes (M2Rs) possessing polyester axles of varying molecular weights. The crystallinity of the axle polymers of two series of M2Rs, with either fixed and movable components, was evaluated by differential scanning calorimetry. The results revealed that the effect of component mobility was significant in the fixed and movable M2Rs with a certain axle length, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components.

Macromolecular [2]rotaxanes comprising a polymer axle and crown ether wheel were synthesized to evaluate the effect of component mobility on the properties of the axle polymer, especially its crystallinity. Living ring-opening polymerization of δ-valerolactone with a pseudorotaxane initiator with a hydroxy group at the axle terminus was followed by end-capping with a bulky isocyanate. This yielded macromolecular [2]rotaxanes (M2Rs) possessing polyester axles of varying molecular weights. The crystallinity of the axle polymers of two series of M2Rs, with either fixed and movable components, was evaluated by differential scanning calorimetry. The results revealed that the effect of component mobility was significant in the fixed and movable M2Rs with a certain axle length, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components.

High-yielding synthesis of cyclic block copolymer (CBC) using the rotaxane protocol by linear-cyclic polymer topology transformation was first demonstrated. Initial complexation of OH-terminated sec-ammonium salt and a crown ether was followed by the successive living ring-opening polymerizations of two lactones to a linear block copolymer having a rotaxane structure by the final capping of the propagation end. CBC was obtained in a high yield by an exploitation of the mechanical linkage through the translational movement of the rotaxane component to transform polymer structure from linear to cyclic. Furthermore, the change of the polymer topology was translated into a macroscopic change in crystallinity of the block copolymer.

Native α-cyclodextrin- (α-CD) and permethylated α-CD (PMeCD)-based rotaxanes with various short alkylene chains as axles can be synthesized through a urea end-capping method. Native α-CD tends to form [3]- or [5]pseudorotaxanes and not [2]- or [4]pseudorotaxanes, which indicates that the coupled CDs act as a single fragment. End-capping reactions of the pseudorotaxanes with C18 and C24 axle lengths do not occur because the axle termini are covered by the densely stacked CDs. The number of PMeCDs on the pseudorotaxane is flexible and mainly depends on the axle length. Peracetylated α-CD (PAcCD)-based rotaxanes are synthesized through O-acetylation of the α-CD-based rotaxanes without any decomposition of the rotaxanated structures. The structures of PMeCD-based [3]- and [4]rotaxanes, and the molecular dynamics calculations on [3]pseudorotaxanes, indicate that the tail face of PMeCDs is regularly directed toward the axle termini. On the basis of the results obtained, it can be concluded that the directions and numbers of CDs in rotaxanes containing short alkylene chains depend on 1) the interactions between CDs, 2) the length of the alkylene axle, and 3) the interactions between the axle end and tail face of the CD.

Topology transformation of a star polymer to a linear polymer is demonstrated for the first time. A three-armed star polymer possessing a mechanical linking of two polymer chains was synthesized by the living ring-opening polymerization of δ-valerolactone initiated by a pseudo[2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with a bulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with a fixed rotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety, which liberated the components from the interaction to move the wheel component to the urethane terminal as the interaction site, eventually affording the linear polymer. The physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity.

Topology transformation of a star polymer to a linear polymer is demonstrated for the first time. A three-armed star polymer possessing a mechanical linking of two polymer chains was synthesized by the living ring-opening polymerization of δ-valerolactone initiated by a pseudo[2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with a bulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with a fixed rotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety, which liberated the components from the interaction to move the wheel component to the urethane terminal as the interaction site, eventually affording the linear polymer. The physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity.

α-Cyclodextrin (CD)-based size-complementary [3]rotaxanes with alkylene axles were prepared in one-pot by end-capping reactions with aryl isocyanates in water. The selective formation of [3]rotaxane with a head-to-head regularity was indicated by the X-ray structural analyses. Thermal degradation of the [3]rotaxanes bearing appropriate end groups proceeded by stepwise dissociation to yield not only the original components but also [2]rotaxanes. From the kinetic profiles of the deslippage, it turned out that the maximum yield of [2]rotaxane was estimated to be 94 %. Thermodynamic studies and NOESY analyses of such rotaxanes revealed that [2]rotaxanes are specially stabilized, and that the dissociation capability of the [3]rotaxanes to the components can be adjusted by controlling the structure of the end groups, direction of the CD groups, and length of the alkylene axle.

To open out new aspects of 9,9-diarylfluorene (DAF)-based polymers with high performances, 9,9-(4-hydroxyphenyl)-4,5-diazafluorene (N-BPF) was designed as a new cardo structure and the properties of poly(ether ketone)s (N-PEKs) containing N-BPF skeletons were examined in detail. N-PEKs were synthesized in high yields via polycondensation of N-BPF with difluoroarenes. N-PEKs showed cardo polymer-specific properties such as high thermal stability and high solubility in organic solvents. The addition of p-toluenesulfonic acid (TsOH) to N-PEK resulted in the formation of network polymer based on interchain hydrogen bonds. It turned out that the films of network polymer are flexible and transparent and exhibit high refractive index and low birefringence. The effects of feed ratio of TsOH to N-PEK were also evaluated on the mechanical properties of network polymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4541–4549

A supramolecular cross-linked cross-linker, capable of introducing rotaxane cross-links to vinyl polymers, has been developed for the rational synthesis of polyrotaxane networks. The experimental results reveal that the combination of an oligocyclodextrin (OCD) and a terminal bulky group-tethering macromonomer (TBM) forms a polymer-network structure having polymerizable moieties through supramolecular cross-linking. Radical polymerization of a variety of typical vinyl monomers in the presence of the vinylic supramolecular cross-linker (VSC) afforded the corresponding vinyl polymers cross-linked through the rotaxane cross-links (RCP) as transparent stable films in high yields under both photoinitiated and thermal polymerization conditions. A poly(N,N-dimethylacrylamide)-based hydrogel synthesized by using VSC, RCP_DMAAm, displayed a unique mechanical property. The small-angle X-ray scattering (SAXS) results, indicating patterns characteristic of a polyrotaxane network, clearly suggested the presence and role of the rotaxane cross-links. The confirmation of the introduction of rotaxane-cross-links into vinyl polymers strongly reveals the significant usefulness of VSC.

Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}₂] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields. Polymers with optically active wheel components that are far from the main chain show no Cotton effect, thereby indicating the formation of racemic helices. Our proposal that N-acylative neutralization of the sec-ammonium moieties of the side-chain rotaxane moieties enables asymmetric induction of a one-handed helix as the wheel components approach the main chain is strongly supported by observation of the Cotton effect around the main-chain absorption region. A polyacetylene with a side-chain rotaxane that has a shorter axle component shows a Cotton effect despite the ammonium structure of the side-chain rotaxane moiety, thereby suggesting the importance of proximity between the wheel and the main chain for the formation of a one-handed helix. Through-space chirality induction in the present systems proved to be as powerful as through-bond chirality induction for formation of a one-handed helix, as demonstrated in an experiment using non-rotaxane-based polyacetylene that had an optically active binaphthyl group. The present protocol for controlling the helical structure of polyacetylene therefore provides the basis for the rational design of one-handed helical polyacetylenes.

Syntheses of 2,2′-bisalcoholic group-substituted 9,9′-spirobifluorene monomers 2 were performed by the reaction of 2,2′-dihydroxy-9,9′-spirobifluorene 2a with haloalcohols. Polycarbonates consisting of 9,9′-spirobifluorene skeleton in the main chain (PC 4) were synthesized by the polycondensation of 2,2′-bisalcoholic monomers 2 and triphosgene or diphenyl carbonate. PC 4 showed good thermal stability: the 5% weight loss temperature was over 330 °C under both nitrogen and air atmospheres. The glass transition temperature was in a range of 16–269 °C estimated by differential scanning calorimetry, depending on the flexibility of the alkylene or oxyethylene chains of 2. PC 4 showed high solubility toward ordinary organic solvents such as CHCl₃, benzene, and THF, making possible the preparation of the flexible thin films. Very high refractive index in a range of 1.62–1.66 at 589 nm was observed although PC 4 consists only of C, H, and O atoms, whereas very low degree of birefringence was confirmed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3658–3667, 2010

Poly(arylene thioether)s (PTEs) containing 9,9′-spirobifluorene moieties were synthesized in high yields from 9,9′-spirobifluorene-2,2′-bis(N,N-dimethylcarbamothioate) 4 as the masked dithiol and various difluoroarenes as electrophilic monomers. All PTEs showed high thermal stability: The 10% weight loss temperature as evaluated by thermogravimetric analysis was over 470 °C under both nitrogen and air atmospheres. The glass transition temperature estimated by DSC was in the range 210–270 °C. The PTEs showed high solubility in ordinary organic solvents, such as CHCl₃, NMP, and THF. Most PTEs exhibited remarkably high refractive indices ranging from 1.69 to 1.73 at 587.6 nm, whereas no or little birefringence was observed for the PTEs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4192–4199, 2010