30 research outputs found

    Preparation of a Library of Poly(<i>N</i>‑sulfonylimidates) by Cu-Catalyzed Multicomponent Polymerization

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    Efficient synthesis of polyimidates has been a great challenge because of the difficulty of imidate bond formation and limited substrate scope. Here, we describe a successful method for the synthesis of various poly­(<i>N</i>-sulfonylimidates) using Cu-catalyzed multicomponent polymerization (MCP). Minimizing water contamination in the polymerization, which results in low-molecular-weight oligomers, allows various combinations of three types of monomers (diynes, sulfonyl azides, and diols) that are bench stable and readily accessible, providing access to a library of polyimidates. Moreover, the formation of polyimidates is highly selective over the conventional click reactions. Most importantly, this report demonstrates a successful MCP that overcomes the drawbacks of previous MCP methods showing narrow monomer scope and producing low-molecular-weight polymers

    Synthesis of Rod-Like Dendronized Polymers Containing G4 and G5 Ester Dendrons via Macromonomer Approach by Living ROMP

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    High generation dendronized polymers with high molecular weight were synthesized by ROMP via macromonomer approach. The polymerization was achieved in living manner and the macromolecules exhibited rod-like conformation. Correlation between the monomer structures and the conformation of the final polymers was investigated in detail. The rigid rod conformation in solution was confirmed by both light scattering and viscometric analysis and the single polymer chains were visualized by AFM

    Unusual Superior Activity of the First Generation Grubbs Catalyst in Cascade Olefin Metathesis Polymerization

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    Recently, we reported a new cascade ring-opening/closing metathesis polymerization of monomers containing two cyclopentene moieties. Several Ru catalysts were tested, but the best polymerization results were unexpectedly obtained using the first-generation Grubbs catalyst (<b>G1</b>). This was puzzling since the second- and third-generation Grubbs catalysts are well-known for their higher activities compared to <b>G1</b>. In order to explain the unique and superior activity of <b>G1</b>, we conducted a series of kinetics experiments for the polymerization of 3,3′-oxydicyclopent-1-ene, a representative monomer of this cascade polymerization, as well as the competition polymerization with cycloheptene using the various Grubbs catalysts. Based on our results, we propose a model in which the differences in the steric hindrance between the different ligands and the monomer determine the selectivity of the catalyst approach to the monomer and, therefore, the extent to which the productive pathway leads to successful cascade polymerization. In short, <b>G1</b> with the smaller ligand showed a high preference for the productive pathway

    Cyclopolymerization To Synthesize Conjugated Polymers Containing Meldrum's Acid as a Precursor for Ketene Functionality

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    Recently, the importance of Meldrum’s acid has been reinvestigated because it serves as a great precursor for ketene generation by thermolysis. In this study, we synthesized conjugated polymers containing Meldrum’s acid via controlled cyclopolymerization using a third-generation Grubbs catalyst. To avoid the solubility issue, copolymerization with soluble monomers was successfully used to provide various random and block copolymers containing Meldrum’s acid in the conjugated backbone. Interestingly, when a polyacetylene derivative containing Meldrum’s acid was incorporated into the second block of the diblock copolymers, highly stable core–shell supramolecules spontaneously formed during the polymerization via in situ nanoparticlization of conjugated polymer. This direct fabrication of nanostructures without requiring any post-treatments was due to the strong π–π interactions and the insolubility of the polyacetylene segment leading to the formation of core in situ. Moreover, thermolysis of Meldrum’s acid to generate ketene in the conjugated polymer core was monitored by IR, and its consecutive cycloaddition to afford the cross-linked core improved the stability of the supramolecules

    Simple Preparation of Various Nanostructures via <i>in Situ</i> Nanoparticlization of Polyacetylene Blocklike Copolymers by One-Shot Polymerization

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    Previously, we reported the one-pot synthesis of polyacetylene (PA) diblock copolymers which formed various nanostructures via the <i>in situ</i> nanoparticlization of conjugated polymers (INCP), using a two-step protocol based on sequential monomer addition. Herein, we report a much simpler one-shot method for nanostructure formation by the synthesis of PA blocklike copolymers. The blocklike copolymers could be prepared by the one-shot ROMP of comonomers with large differences in their reactivities because the monomers that formed the first block, namely norbornene (NB) derivatives or <i>endo</i>-tricyclo­[4.2.2.0]­deca-3,9-diene (TD) derivatives, polymerized much faster than the monomers that formed the second PA block, cyclooctatetraene (COT). Owing to their blocklike microstructures, the copolymers formed various nanostructures such as nanospheres, nanocaterpillars, and nanoaggregates depending on the chemical structures of the soluble shell polymers and feed ratio of COT, which formed the insoluble PA core. Using dynamic light scattering (DLS) and atomic force microscopy (AFM), it was observed that the nanostructures produced from the blocklike copolymers were essentially the same as those produced from the block copolymers synthesized by conventional sequential monomer addition. The blocklike microstructures of the copolymers formed by one-shot ROMP were further supported by an <i>in situ</i> <sup>1</sup>H NMR kinetic experiment and UV/vis spectroscopy. From these results, we were able to confirm that the ROMP of TD and COT produced near-perfect block copolymers. Furthermore, the <sup>1</sup>H NMR spectra of the one-shot copolymerization provided insights into the INCP process

    Tandem Ring-Opening/Ring-Closing Metathesis Polymerization: Relationship between Monomer Structure and Reactivity

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    Monomers containing either cycloalkenes with low ring strain or 1-alkynes are poor monomers for olefin metathesis polymerization. Ironically, keeping two inactive functional groups in proximity within one molecule can make it an excellent monomer for metathesis polymerization. Recently, we demonstrated that monomer <b>1</b> having cyclohexene and propargyl moieties underwent rapid tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization via relay-type mechanism. Furthermore, living polymerization was achieved when a third-generation Grubbs catalyst was used. Here, we present a full account on this tandem polymerization by investigating how various structural modifications of the monomers affected the reactivity of the tandem polymerization. We observed that changing the ring size of the cycloalkene moieties, the length of the alkynes, and linker units influenced not only the polymerization rates but also the reactivities of Diels–Alder reaction, which is a post-modification reaction of the resulting polymers. Also, the mechanism of tandem polymerization was studied by conducting end-group analysis using <sup>1</sup>H NMR analysis, thereby concluding that the polymerization occurred by the alkyne-first pathway. With this mechanistic conclusion, factors responsible for the dramatic structure–reactivity relationship were proposed. Lastly, tandem RO/RCM polymerization of monomers containing sterically challenging trisubstituted cycloalkenes was successfully carried out to give polymer repeat units having tetrasubstituted cycloalkenes

    Controlled Ring-Opening Metathesis Polymerization of a Monomer Containing Terminal Alkyne and Its Versatile Postpolymerization Functionalization via Click Reaction

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    Controlled Ring-Opening Metathesis Polymerization of a Monomer Containing Terminal Alkyne and Its Versatile Postpolymerization Functionalization via Click Reactio

    Cu-Catalyzed Multicomponent Polymerization To Synthesize a Library of Poly(<i>N</i>‑sulfonylamidines)

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    We report a versatile Cu-catalyzed multicomponent polymerization (MCP) technique that enables the synthesis of high-molecular-weight, defect-free poly­(<i>N</i>-sulfonylamidines) from monomers of diynes, sulfonyl azides, and diamines. Through a series of optimizations, we discovered that the addition of excess triethylamine and the use of <i>N</i>,<i>N</i>′-dimethylformamide as a solvent are key factors to ensure efficient MCP. Formation of cyclic polyamidines was a side reaction during polymerization, but it was readily controlled by using diynes or diamines with long or rigid moieties. In addition, this polymerization is highly selective for three-component reactions over click reactions. The combination of the above factors enables the synthesis of high-molecular-weight polymers, which was challenging in previous MCPs. All three kinds of monomers (diynes, sulfonyl azides, and diamines) are readily accessible and stable under the reaction conditions, with various monomers undergoing successful polymerization regardless of their steric and electronic properties. Thus, we synthesized various high-molecular-weight, defect-free polyamidines from a broad range of monomers while overcoming the limitations of previous MCPs, such as low conversion and defects in the polymer structures

    Brush Polymers Containing Semiconducting Polyene Backbones: Graft-Through Synthesis via Cyclopolymerization and Conformational Analysis on the Coil-to-Rod Transition

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    Using a grafting-through strategy, brush polymers containing semiconducting polyene backbones were efficiently synthesized by cyclopolymerization for the first time. Macromonomers containing poly­(l-lactide) and poly­(ε-caprolactone), prepared by living ring-opening polymerization, were polymerized using the Grubbs–Hoveyda catalyst to produce high molecular weight (>0.5 M Da) brush polymers. The brush polymers underwent a unique coil-to-rod transition during the aging of the polymer solution, and this conformational change was supported by UV–vis and size-exclusion chromatography (SEC)–viscometry analysis. In addition, the extended conformation of single chains of the brush polymers could be visualized by atomic force microscopy

    Cascade Polymerization via Controlled Tandem Olefin Metathesis/Metallotropic 1,3-Shift Reactions for the Synthesis of Fully Conjugated Polyenynes

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    We demonstrate the first example of cascade polymerization by combining olefin metathesis and metallotropic 1,3-shift reactions to form unique conjugated polyenynes. Rational design of monomers enabled controlled polymerization, and kinetic investigation of the polymerization mechanism was conducted
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