| POLYMERS Vol.70 No.9 |
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COVER STORY
Power of Ladder Structure: Two Bonds Are Mightier Than One Bond |
| COVER STORY: Highlight Reviews |
| Ladder-Shape π-Conjugated Molecules | Hayato TSUJI, Eiichi NAKAMURA |
| <Abstract> Construction of ladder-type molecular structures has received much attention over years as an efficient methodology to improve the properties and stability of π-conjugated molecules. In this article, recent examples of poly/oligophenylene-type and poly/oligophenylenevinylene-type π-conjugated ladder molecules and their representative applications will be introduced. Keywords: Coordination Bond / Hydrogen Bond / Covalent Bond / Intramolecular Cross-Linkage / Oligophenylene / Oligophenylenevinylene / Ladder-Type Molecules / π-Conjugation |
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| Chemistries for Ladder Polymerization | Hiroaki SHIMOMOTO, Yan XIA |
| <Abstract> Ladder polymers have distinctive structures of a sequence of fused rings, leading to rigid conformations and unusual properties that may be inaccessible by traditional linearly linked polymers. Ladder chains are fascinating polymer architectures, but their synthesis is challenging and requires highly efficient and selective chemistry. We highlight the main chemistries developed for the synthesis of ladder polymers via ladder polymerization. Keywords: Ladder Polymer / Ladder Polymerization |
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| COVER STORY: Topics and Products |
| Conjugated Ladder Polymer Synthesis through New Polymer Reaction | Koji TAKAGI |
| <Abstract> Conjugated ladder polymers have unique optoelectronic characteristics because of the restricted conformational freedom, but their efficient syntheses are less explored compared with those of non-ladder conjugated polymers. Herein we describe the defect-less conjugated ladder polymer synthesis through new polymer reactions by means of the stereochemistry of functional groups in the precursor polymer. First, ladder poly-p-phenylene was synthesized from N-alkylated poly(aromatic amide) by utilizing the cis preference of tertiary aromatic amide and the palladium-catalyzed direct arylation. The obtained ladder polymer exhibited a marked p-stacking behavior. The similar methodology was applied for the synthesis of ladderized polystyrene to reveal the importance of the main chain conformation of the precursor polymer. Second, the ladderization of poly-p-phenylenevinylene was investigated by the oxidative coupling between the trans C=C vinylene group in the main chain and the aryl ring at the side chain. Although the ladder efficiency was not perfect, this approach will be also applicable for the synthesis of conjugated ladder polymers. Keywords: Conjugated Polymer / Ladder Polymer / Polymer Reaction / Direct Arylation / Oxidative Coupling |
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| Fascinating Helical Ladder Polymers | Tomoyuki IKAI |
| <Abstract> The construction of helical ladder-shaped architectures is not even a challenge in a macroscopic level like building toys, but it’s a totally different story when it comes to a molecular level. Thus, the development of a versatile methodology to produce synthetic ladder polymers with desired primary and secondary structures in a predictable manner is still challenging. But the latter may hold great potential for leading to dramatic innovations in the next-generation optoelectronic materials arising from their rigid and robust frameworks. Herein we report an unprecedented synthesis of well-defined single-handed helical ladder polymers that can be applied to chiral materials, such as chiral stationary phases and circularly polarized luminescence materials, through quantitative and chemoselective intramolecular alkyne benzannulations of random-coil precursor polymers. The presented results will provide the potential for realizing the defect-free precise synthesis of further varieties of fully-conjugated ladder-type molecules, polymers, and graphene nanoribbons with unique helical, coplanar, and zig-zag geometries in a predictable manner by the rational molecular design of cyclization precursors. Keywords: Alkyne Benzannulations / Chirality / Chemoselectivity / CPL / Helix / Spiro-Conjugation |
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| Synthesis of Polymers with a Ladder Repeating Unit by New Reactions | Ryo SHINTANI |
| <Abstract> A new mode of polymerization, rhodium-catalyzed stitching polymerization, has been developed for the synthesis of π-conjugated polymers with a ladder-type repeating unit from non-conjugated 1,5-hexadiynes containing both terminal and internal alkyne moieties as monomers. The polymerization proceeded smoothly in the presence of [Rh(OH)(cod)]2 as the catalyst to give the corresponding stitched polymers under mild conditions, and 1,5,9-decatriyne and 1,5,9,13-tetradecatetrayne monomers could also be employed. This polymerization strategy is particularly beneficial for the synthesis of polymers consisting of a repeating unit that is difficult to prepare as a stable monomer because it does not require the use of a preformed ladder-type π-conjugated monomer. Keywords: Stitching Reaction / Stitching Polymerization / Rhodium Catalyst / Alkyne |
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| Production of Carbon Fiber from Rigid and Linear Polymers | Toshihira IRISAWA |
| <Abstract> Carbon fibers are important materials because of their low environmental impact when they are used as reinforced fibers for CFRPs. However, carbon fiber has a serious problem regarding its cost. The high cost of carbon fiber is due to the use of polyacrylonitrile as a precursor, and the development of low-cost carbon fiber is being carried out in many countries worldwide. In this background, the author has been developing carbon fibers using rigid and linear polymers as precursors. By using these polymers as precursors, a simple carbon fiber production process could be realized without the need for preliminary oxidative treatment. We regard these developments as the first step in the realization of low-cost carbon fiber, and will continue to develop them in the future. Keywords: Carbon Fiber / New Precusor / Low-Cost |
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| Design, Synthesis, and Evaluation of Function of Ladder-Shaped Polyethers | Tohru OISHI |
| <Abstract> Ladder-shaped polyethers (LSPs) produced by dinoflagellates are thought to bind to transmembrane (TM) proteins. To elucidate the interactions of LSPs with TM proteins, artificial ladder-shaped polyethers (ALPs) containing 6/7/6-fused iterative system were designed, and tetracyclic-, heptacyclic-, and decacyclic-ALPs were systematically synthesized based on the convergent method via α-cyano ethers. The interaction between ALPs and TM proteins was evaluated by dissociation of glycophorin A (GpA) dimers into monomers. The interaction motif of GpA dimers is a glycine zipper, in which hydrogen bonds between the Cα–H of glycine and the carbonyl oxygen are stabilizing the dimeric structure. A similar interaction could be also expected between the Cα–H of glycine and skeletal oxygen atoms of ALPs as a hydrogen bond acceptor. Recently, protein-protein interactions (PPIs) attract attentions in drug discovery. Because of the affinity with TM proteins, ALPs are expected to be inhibitors of PPIs in TM proteins. Therefore, development of efficient synthetic methods of ALPs is an important issue and is in progress. Keywords: Ladder-Shaped Polyether / Design and Synthesis / Convergent Strategy / Membrane Protein / α-Helix / Glycine Zipper / Cα–H…O Hydrogen Bonding / Protein–Protein Interaction |
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| Polymer Science and I: A Personal Account |
| Heartfelt Thanks | Hajime SHIGEMITSU |
| <Abstract> Whenever I changed my environment, I faced various problems and overcame the walls with the support of many people. This article introduces the history of my struggle in chemistry. |
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| Front-Line Polymer Science |
| C-H Functionalization Strategies for the Synthesis of π-Conjugated Polymers | Junpei KUWABARA, Takaki KANBARA |
| <Abstract> π-Conjugated polymers serve as key materials in organic optoelectronic devices. Polycondensation using C-H direct arylation has become a promising sustainable alternative to the conventional cross-coupling polycondensation reactions for the synthesis of π-conjugated polymers because the utilization of C-H functionalization can eliminate the prefunctionalization steps for C-C bond formation. To enhance utility for the strategy, development to ensure a high reliability in an accurate recurring structure of products and a wide range of application comparable to the conventional methods have been investigated. Besides, efficient synthetic protocols that take into account the concerns regarding cost and environment have been developed. This review describes recent activities on the efficient synthesis of π-conjugated polymers via direct arylation (C-H/C-X coupling) and cross-dehydrogenative coupling (C-H/C-H coupling) reactions. Keywords: Conjugated Polymer / Direct Arylation / C-H Functionalization / Polycondensation / Organic Semiconductors |
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