| POLYMERS Vol.72 No.6 |
| >> Japanese | >> English |
COVER STORY
Elucidation of Polymerization Reactions and Efforts to Precisely Control Structures |
| COVER STORY: Highlight Reviews |
| Rapid Synthesis of Middle-Size Biomolecules Comprising of a Repeating Structure | Yasuhito KOYAMA |
| <Abstract> Synthesis of natural products with medium molecular weights usually requires multi-step synthesis. The labor-saving and large scale synthetic methods of producing middle-sized biomolecules have been extensively studied for the evaluation of properties and practical applications. This paper describes the syntheses of middle-sized biomolecules comprising of a repeating structure such as polypeptides, deoxypropionates, poly(cyclic ether)s, oligosaccharides, glycosides, terpenoids, and polyketides. The syntheses of middle-sized biomolecules have been achieved by synthetic approaches from not only small molecular but also macromolecular chemistry. With this compilation at hand, some precise polymerization techniques might be applied to develop rapid synthetic methods for the syntheses of middle-sized biomolecules in the future. Keywords: Middle-Size Biomolecules / Polypeptide / Deoxypropionate / Poly(Cyclic Ether) / Oligosaccharide / Glycoside / Terpenoid / Polyketide |
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| Advances in Polymerization of Aromatic Acetylenes | Tsuyoshi TANIGUCHI, Tatsuya NISHIMURA, Katsuhiro MAEDA |
| <Abstract> The development of well controlled polymerization of acetylenes is essential for the application of polyacetylenes to functional materials. There have been serious problems, such as difficult functionalization of polymer terminals and limited scope of monomers, in conventional polymerization methods. The present paper focuses on recent studies of polymerization of aromatic acetylenes to overcome such problems. First, we highlight living polymerization of phenylacetylenes enabling versatile functionalization of polymer terminals using rhodium catalysis and aromatic boronic acids. Second, we present the mechanism elucidation and improvement of polymerization of diphenylacetylenes induced by tungsten and tantalum catalytic systems. Keywords: Polyacetylenes / Polymerization / Living Polymerization / Polymerization Mechanism / Rhodium / Tungsten / Tantalum |
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| Organic Synthesis of Medium Molecules: Electrochemical Amide Bond Formations | Yohei OKADA |
| <Abstract> “Medium molecules” have been recognized as promising therapeutic candidates and their chemical synthesis is of great importance in the field of medicinal chemistry. Peptides are representative examples of this class, and their synthesis is usually carried out by a solid-phase method using insoluble resins as supports. Recently, a liquid-phase method using “soluble tags” as supports has also been paid a considerable attention to synthesize peptides, especially in larger scale. Several tags have been proposed so far to realize practical peptide syntheses in liquid phase, which enjoy typical analytical techniques, including nuclear magnetic resonance and mass spectroscopies, and thin-layer column chromatography. This is advantageous for “organic synthesis” of peptides, since a usual reaction monitoring is possible to confirm the completion at each step. In this account, recent organic synthesis of peptides is introduced in combination with electrochemical amide bond formations using triphenyl phosphine as a potentially recyclable coupling agent. The anodically generated phosphine radical cation can activate carboxylic acids under mild conditions. Keywords: Organic Synthesis / Medium Molecule / Electrochemistry / Amide Bond Formation / Peptide / Liquid Phase / Soluble Tag |
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| COVER STORY: Topics and Products |
| Simultaneous Control of Molecular Weights and Stereo-Strctures by Degenerative Chain-Transfer Cationic Polymerizations | Mineto UCHIYAMA |
| <Abstract> Recently, we developed novel living cationic polymerizations that proceed via degenerative chain-transfer (DT) mechanisms using thioesters and thioethers as reversible chain-transfer agents in the presence of various cationic initiators. This article describes our recent research about the simultaneous control of molecular weight and stereo-structures using cationic reversible addition-fragmanetation chain transfer (RAFT) or DT polymerizations. Stereospecific cationic RAFT polymerization was achieved by combining cationic RAFT polymerization with thioesters and stereospecific cationic polymerization of bulky vinyl ethers with Lewis acid catalysts. The molecular weight was controlled by the RAFT process whereas the tacticity was controlled by stereospecific propagation based on the steric hindrance of bulky side groups and counteranions derived from the Lewis acid catalyst. In addition, the cationic DT process is also applicable to asymmetric cationic polymerization of benzofuran by combination of Lewis acid catalysts and chiral additives to achieve the dual control of molecular weight and optical activity of the resulting polymers. Keywords: Living Polymerization / Cationic Polymerization / Degenerative Chain-Transfer / RAFT Polymerization / Stereospecific Polymerization / Poly(vinyl Alcohol) / Asymmetric Polymerization / Benzofuran |
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| Design of Photocatalysts for Polymer Synthesis Using Visible-Light as External Stimulus | Akiko INAGAKI |
| <Abstract> In the field of homogeneous catalysis, various efficient photoredox reactions have been developed, in which mainly ruthenium and iridium visible-light sensitizers play the key roles in the catalysis to promote single electron transfer to generate reactive radical species under mild conditions. Apart from these reactions, utilization of the excited-state of the catalyst itself may lead to new type light-controlled reactions. In order to realize such reactions, precise design of the photocatalysts is inevitable for the efficient formation of the desired excited-state. Our intensive studies on developing new visible-light driven catalysts are described here. Utilization of a bichromophore unit in order to extend the excited-state lifetime was successful to realize high reactivity of the Ir-Pd catalyst toward styrene polymerization. Visible-light irradiation intensively drives the polymerization because of producing a highly active excited state for monomer insertion. The character of the catalyst can be used to tune the copolymerization reaction to yield copolymers with different co-monomer content and glass-transition temperature. Keywords: Visible-Light Energy / Photocatalyst / Dinuclear Catalyst / Photosensitizer / Bichromophore / Polymerization / Excited-State Lifetime / Ruthenium / Iridium / Copper Photosensitizers |
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| One-Pot Synthesis of Sequence-Controlled Oligosiloxanes | Kazuhiro MATSUMOTO |
| <Abstract> A wide variety of sequence-defined oligosiloxanes can be synthesized by one-pot controlled iteration of B(C6F5)3-catalyzed dehydrocarbonative condensation of alkoxysilanes with hydrosilanes and hydrosilylation of carbonyl compounds. Keywords: Oligosiloxanes / Siloxanes / One-Pot Synthesis / Controlled Iteration |
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| Polymer Science and I: A Personal Account |
| Number of Moves | Keiji MURAYAMA |
| <Abstract> I believe that the most important point for research is the number of experiments carried out. I performed a lot of experiments as a student, which resulted in successful development of novel Xeno Nucleic Acids. No one can accurately predict the results. The number of experiments promises the success. |
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| Front-Line Polymer Science |
| Multicomponent Supramolecular Nanobiomaterials | Sayuri L. HIGASHI, Masato IKEDA |
| <Abstract> Biomolecular assemblies inside living cells have inspired us to design self-assembling molecules capable of showing orthogonal self-assembly and/or stimuli-responsive and energy dissipative self-assembling phenomena, which may lead to the construction of intelligent supramolecular nanobiomaterials as well as artificial cells. Here, we highlight recent papers including those from our group, in which research on the two topics, i.e., orthogonal/dissipative self-assembly, with synthetic self-assembling molecules have been conducted. Keywords: Supramolecular Materials / Self-Assembly / Nanostructures / Orthogonal / Dissipative / Biomolecular Sciences |
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