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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]

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]

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. [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]

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]

[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]

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]

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]

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]

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 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]