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We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A pentacyclic quadruply fused polymer topology has been constructed for the first time through alkyne-azide addition (click) and olefin metathesis (clip) reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process. Thus, a spiro-type, tandem tetracyclic poly(tetrahydrofuran), poly(THF), precursor having two allyloxy groups at the opposite positions of the four ring units was prepared by the click-linking of one unit of an eight-shaped precursor having alkyne groups at the opposite positions with two units of a single-cyclic counterpart having an azide and an alkene group at the opposite positions. Both are obtainable through ESA-CF. The subsequent metathesis clip-folding of the tetracyclic precursor could afford a pentacyclic quadruply fused polymer product, of "shippo" form, in 19% yield., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Unprecedented tetracyclic polymer topologies with spiro- and a bridged-type quatrefoil forms are effectively constructed through an alkyne-azide, click-linking reaction by employing a kyklo-telechelic poly(tetrahydrofuran), poly(THF), precursor having an azide group, obtained through an electrostatic self-assembly and covalent fixation (ESA-CF) process, and complementary tetrafunctional alkyne reagents of either a pentaerythritol derivative or a four-armed star telechelic polymer precursor., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.

A regioselective nucleophilic esterification upon six-membered, thus considered unstrained, azacyclohexane quaternary salts has been disclosed by DFT calculations using a model compound and subsequent experimental studies of nucleophilic substitution on N-phenyl-3,3-dimethylpiperidinium salt groups at the polymer chain ends by carboxylate anions. An exclusive ring-emitting esterification was proposed theoretically and confirmed experimentally to produce a simple ester group, in contrast to less robust amino-ester linkages through an alternative ring-opening process with strained five-membered ammonium salts. This reaction was subsequently applied to a prototypical process of an electrostatic self-assembly and covalent fixation (ESA-CF) technique to produce a ring polymer having simple ester linking units.

A tandem alkyne-azide addition, i.e., click, and an olefin metathesis condensation, i.e., clip, reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process, have been demonstrated as effective means to produce constructions of programmed folding of polymers having doubly fused tricyclic and triply fused tetracyclic topologies. Thus, a series of cyclic poly(tetrahydrofuran), poly(THF), precursors having an allyloxy group and an alkyne group (Ia), an allyloxy group and an azide group (Ib), and two alkyne groups (Ic) at the opposite positions was prepared by means of the ESA-CF method. The subsequent click reactions of Ia with a linear telechelic poly(THF) precursor having azide end groups (Id) and of Ib with Ic afforded a bridged dicyclic polymer (IIa) and a tandem spiro tricyclic precursor (IIb), respectively, both having two allyloxy groups at the opposite positions of the ring units. Finally, the intramolecular metathesis condensation reaction of IIa and of IIb in the presence of a Grubbs catalyst was performed to construct effectively a doubly fused tricyclic and a triply fused tetracyclic polymer topologies (III and IV), respectively., (© 2011 American Chemical Society)

Newly designed norbornene-appended hexabenzocoronene 1 self-assembles, upon diffusion of an Et(2)O vapor into its CH(2)Cl(2) solution, to form either graphitic nanocoils or nanotubes, depending on the self-assembling conditions. The coiled assembly, selectively formed at 15 degrees C, is a kinetic intermediate for the tubular assembly and transforms into nanotubes on standing at 25 degrees C. However, post-ring-opening metathesis polymerization of the norbornene pendants of 1 enhances the thermal stability of the coiled assembly as well as the tubular one and disables a thermodynamic coil-to-tube transition. The polymerized nanocoils show an electroconductivity of 1 x 10(-)(4) S cm(-)(1) upon doping with I(2), while the nonpolymerized nanocoils are disrupted upon being doped.

Recently, experimental investigations of a class of temperature-responsive polymers tethered to oligooxyethylene side chains terminated with alkyl groups have been conducted. In this study, aqueous solutions of poly(glycidyl ether)s (PGE) with varying numbers of oxyethylene units, poly(methyl(oligooxyethylene)n glycidyl ether) (poly(Me(EO)nGE)), and poly(ethyl(oligooxyethylene)n glycidyl ether) (poly(Et(EO)nGE) (n = 0, 1, and 2) were investigated by all-atom molecular dynamics simulations, focusing on the thermal responses of their chain extensions, the recombination of intrapolymer and polymer–water hydrogen bonds, and water-solvation shells around the alkyl groups. No clear relationship was established between the phase-transition temperature and the polymer-chain extensions unlike the case for the coil–globule transition of poly(N-isopropylacrylamide). However, the temperature response of the first water-solvation shell around the alkyl group exhibited a notable correlation with the phase-transition temperature. In addition, the temperature at which the hydrophobic hydration shell strength around the terminal alkyl group equals the bulk water density ( T CRP ) was slightly lower than the cloud point temperature ( T CLP ) for the methyl-terminated poly(Me(EO)nGE) and slightly higher for the ethyl-terminated poly(Et(EO)nGE). It was concluded that the polymer-chain fluctuation affects the relationship between T CRP and T CLP . [ABSTRACT FROM AUTHOR]

The purification step in the manufacturing of cyclic polymers is difficult as complete fractionation to eliminate linear impurities requires considerable effort. Here, we report a new polymer separation methodology that uses metal‐organic frameworks (MOFs) to discriminate between linear and cyclic polyethylene glycols (PEGs) via selective polymer insertion into the MOF nanopores. Preparation of a MOF‐packed column allowed analytical and preparative chromatographic separation of these topologically distinct pairs. In addition, gram‐scale PEGs with only cyclic structures were successfully obtained from a crude reaction mixture by using MOF as an adsorbent. [ABSTRACT FROM AUTHOR]

Abstract Since polymers of cyclic topology have no main chain terminus, and the conformation is limited, they show physical and chemical properties different from those of linear polymers even the composition and molecular weight are the same. In order to pursue functions based on the topology of polymers, we have developed synthetic methods for cyclic polymers and constructed nanostructures by self-assembly. As a result, it was found that micelles and vesicles formed by cyclic polymers exhibit characteristics, which were greatly changed as compared with those of linear polymers. Based on cyclic-to-linear transformation, a gelling agent was developed, and furthermore, the reversible and repeatable topological conversion was achieved. Moreover, monolayer assemblies such as self-assembled monolayers on a gold surface and Langmuir–Blodgett films were constructed from cyclic macromolecules. [ABSTRACT FROM AUTHOR]

This study demonstrates the comprehensive investigation on the reversible linear-cyclic topological conversion of hydrophilic and hydrophobic polymers with various molecular weights. The reactions were triggered by light or heat, which reversibly dimerize and cleave the anthryl or coumarinyl end groups of the telechelics. Poly(ethylene oxide) telechelics with anthryl end groups attached through electron-donating (Ant-O-PEO and Ant-CH2-PEO) and electron-withdrawing (Ant-CO2-PEO) linking groups were synthesized. While Ant-O-PEO and Ant-CH2-PEO decomposed upon photoirradiation at 365 nm, Ant-CO2-PEO efficiently cyclized through the photodimerization of the anthryl end groups both in water and in organic solvents shown by NMR, SEC, and MALDI-TOF MS. The lower the molecular weight, the faster the cyclization proceeded. When cyclized Ant-CO2-PEO was heated at 150 °C in bulk, the polymers quantitatively converted back into the original linear topology. Furthermore, repeatable linear-cyclic topological conversion was confirmed. The reversible topological conversion of hydrophobic poly(tetrahydrofuran) telechelics with anthryl end groups (Ant-PTHF) was also successful. In addition, poly(ethylene oxide) telechelics with coumarinyl end groups (Cou-PEO) were also cyclized by irradiation at 365 nm in water. However, the cyclization hardly occurred when performed in methanol likely due to the lack of sufficient hydrophobic interaction of the coumarinyl end groups. Cyclized Cou-PEO was irradiated at 254 nm to test for linearization, finding the linear product and cyclic precursor were likely photoequilibrated. [ABSTRACT FROM AUTHOR]

ABSTRACT The 'topological polymer chemistry' of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB-type diblock and ABA-type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed-phase temperature-dependent behaviors were observed in surface pressure-area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA-type triblock linear copolymers adopted a fiber-like surface morphology via two-dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature-controlled out-of-plane X-ray diffraction (XRD) analysis of Langmuir-Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat-resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher-order reflections ( d002, d003) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 486-498 [ABSTRACT FROM AUTHOR]

A pentacyclic quadruply fused polymer topology has been constructed for the first time through alkyne-azide addition (click) and olefin metathesis (clip) reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process. Thus, a spiro-type, tandem tetracyclic poly(tetrahydrofuran), poly(THF), precursor having two allyloxy groups at the opposite positions of the four ring units was prepared by the click-linking of one unit of an eight-shaped precursor having alkyne groups at the opposite positions with two units of a single-cyclic counterpart having an azide and an alkene group at the opposite positions. Both are obtainable through ESA-CF. The subsequent metathesis clip-folding of the tetracyclic precursor could afford a pentacyclic quadruply fused polymer product, of 'shippo' form, in 19 % yield. [ABSTRACT FROM AUTHOR]

Abstract: Ongoing challenges in topological polymer chemistry are reviewed. In particular, we focus on recent developments in an “electrostatic self-assembly and covalent fixation (ESA–CF)” process in conjunction with effective linking/cleaving chemistry including a metathesis process and an alkyne–azide click reaction. A variety of novel cyclic polymers having specific functional groups and unprecedented multicyclic macromolecular topologies have been realized by combining intriguing synthetic protocols. [Copyright &y& Elsevier]

In this study, we investigate structures and stabilities of the micelles of a cyclic amphiphile (c-PBA-b-PEO) composed of poly(n-butyl acrylate) (PBA) and poly(ethylene oxide) (PEO) blocks and its linear diblock and triblock analogues (l-PBA-b-PEO and l-PBA-b-PEO-b-PBA) by using synchrotron X-ray scattering and quantitative data analysis. The comprehensive scattering analysis gives details and insights to the micellar architecture through structural parameters. Furthermore, this analysis provides direct clues for structural stabilities in micelles, which can be used as a good guideline to design highly stable micelles. Interestingly, in water, all topological polymers are found to form ellipsoidal micelles rather than spherical micelles; more interestingly, the cyclic polymer and its linear triblock analog make oblate-ellipsoidal micelles while the linear diblock analog makes a prolate-ellipsoidal micelle. The analysis results collectively inform that the cyclic topology enables more compact micelle formation as well as provides a positive impact on the micellar structural integrity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermoresponsive block polyglycidylethers are expected to be used as biomaterials. • MD simulations of two polymer chains have been employed to understand the structural transition of thermoresponsive polymers and interpolymer arrangements. Block copolymers are expected to be applied in a wide variety of fields due to the property of self-assembly. Our group has reported that poly(glycidyl ether) block copolymers exhibited complex temperature response in aqueous solution. In this study, we investigated the two chains of the block copolymer structure and configurations at different temperatures by using MD simulation. The results showed that at low temperatures, the polymer structure is linear and can form micelles, but above a certain temperature, the polymer structure changes to a U-shape and the micelle structure would be destroyed, which is responsible for the complex temperature response. [ABSTRACT FROM AUTHOR]

A dicyclic, eight-shaped and a tricyclic,trefoil-shaped poly(THF)both having an alkyne group at the core position (IIand III, respectively) have been introduced as versatile core-clickable kyklo-telechelic precursors. The prepolymer IIhas been prepared by an ESA-CF (electrostatic self-assembly andcovalent fixation) process using an assembly (1a/2b),composed of two units of linear poly(THF) having N-phenylpyrrolidinium salt groups carrying one unit of a tetrafunctionalcarboxylate having an alkyne group as a counteranion. Alternatively,the prepolymer IIIhas been produced through a clickprocess using a cyclic poly(THF) precursor havingan azide group (Ia), obtainable also by the ESA-CF technique,with a tripropargylated pentaerythritol derivative (2c) followed by the esterification with 4-pentynoic acid to introduceagain an alkyne group. The subsequent clickcouplingreaction of IIand IIIwith a linear telechelicpoly(THF) having azide groups (1b) afforded successfullynovel tetra- and hexacyclic bridged-spirohybridpolymer topologies, i.e., double-eight and double-trefoil constructions. [ABSTRACT FROM AUTHOR]