| POLYMERS Vol.70 No.12 |
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COVER STORY
The Ring |
| COVER STORY: Highlight Reviews |
| Polymers with Various Topologies and Physics | Tetsuo DEGUCHI |
| <Abstract> The topology of a ring polymer is described by a knot. The knot type of a ring polymer is kept constant in thermal fluctuations. The entropy of a ring polymer with a fixed knot corresponds to the logarithm of the probability for the ring polymer to have the fixed knot type. We call the probability the knotting probability. Recently, a sum rule has been found with respect to the knotting probabilities of the ring polymer. In order to explain it we introduce some technical terms of knot theory. We then review briefly the research history of ring polymers and knotted DNA. We finally comment on the research prospects of knotted ring polymers to be extended to those of topological polymers and polymer networks. Keywords: Ring Polymer / Knot / DNA / Knotting Probability / Sum Rule |
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| Efficient Construction of Cyclic Polymers Enabled by Precise Polymerization and Cyclizations | Yoshinobu MATO, Takuya ISONO, Toshifumi SATOH |
| <Abstract> Recent progress in precision polymerization has made it possible to synthesize a wide variety of macromolecular architectures, including star, comb, cyclic, and multicyclic polymers, with well-defined structures and narrow dispersity. Among them, the cyclic polymers are of particular interest due to their unique properties, such as ultralubricity on surfaces and bigger micellar thermal stability compared to the linear counterparts, which stems from the lack of chain-ends. In this context, the physical properties and functions of multicyclic polymers having more than two macrocyclic units in a molecule are of considerable interest as of late. This paper gives an overview of the synthetic approaches to cyclic and multicyclic polymers. In addition, we describe the state-of-the-art advancement of multicyclic polymer synthesis based on a consecutive cyclization strategy. Keywords: Polymer Topology/ Cyclic Polymer / Multicyclic Polymer / Precision Polymerization / Consecutive Cyclization |
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| COVER STORY: Topics and Products |
| Ring-Expansion “Vinyl” Polymerization | Atsushi NARUMI |
| <Abstract> Ring-expansion “vinyl” polymerization remains an unestablished methodology in polymer synthetic chemistry in which vinyl monomers are inserted into the backbones of ring-shaped molecules via addition polymerizations. We have projected to utilize the nitroxide-mediated controlled radical polymerization (NMP) to develop such polymerizations. Alkoxyamine derivatives were tethered to produce cyclic NMP initiators, which were used for the polymerizations of styrene (St). In addition to the featured characteristics of the polymerizations, we have explored model reactions among the cyclic NMP initiators and also the brush-modification and subsequent AFM observations. In particular, the microscopic data allowed to quantitatively discuss the details of the reactions taking place in the present system, such as the ring-expansion “vinyl” polymerizations generating cyclic polymers, the fusion of cyclic polymers to form multimers, and their scissions to form linear species. The author expects these outcomes will lead to an advanced morphology-controlled polymerization method to incorporate significant values to the conventional vinyl polymers. Keywords: Polymer Synthesis / Ring-Expansion Polymerization / Controlled Radical / Polymerization / Cyclic Initiator / Macrocyclic Polymer / Multimer / Morphology / Atomic Force Microscopy (AFM) |
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| Linear/Cyclic Topology Transformation of Polymers | Kazuko NAKAZONO |
| <Abstract> The recent development of reversible linear-cyclic polymer structural transformation is reviewed. The conversion of linear and cyclic polymer topologies involves the process of efficient transforming to the cyclic topology by reactions between the ends of the telechelic polymer and to the linear topology by selective bond breaking to generate the initial telechelic polymer. In order to carry out such polymer reactions efficiently, dynamic covalent bond chemistry and reversible covalent bond formation by photo and thermally controlled reactions are utilized. Furthemore, environmentally responsive linear-cyclic polymer structural conversions have also been achieved by using non-covalent bonds such as hydrogen bonds and host-guest complexes as reversible bonds. Finally, recent advances of a new linear-cyclic structure conversion method utilizing the dynamic properties of macromolecular rotaxanes without using the conventional ring closing process is also described. Keywords: Cyclic Polymer / Polymer Topology / Reversible Topologyical / Transformation/Rotaxane |
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| Mathematical Analysis of the Topology of Cyclic Polymers | Koya SHIMOKAWA |
| <Abstract> In this article, we will discuss the topology of cyclic and multicyclic polymers. There are two aspects to the topology of polymers. One is the graph theoretical aspect, which reveals the intrinsic topology of polymers arising from the connection structure consisting of branch points and linear chains. Using graph theory, we will discuss the nomenclature of graphs corresponding to multicyclic polymers. The other is the knot theoretic aspect, which describes its extrinsic topology, the 3-dimensional shape of polymers. The structure of knots, links, and spatial graphs will reveal properties such as topological stereoisomerism and topological chirality. Recently, very complex molecular structures made of links have been constructed and will be reported. Keywords: Cyclic Polymer / Multicyclic Polymer / Topology / Knot / Link / Catenane / Graph / Spatial Graph |
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| Rolling Circle Translation of Circular RNA | Yuko NAKASHIMA, Kosuke FUKUCHI, Naoko ABE, Hiroshi ABE |
| <Abstract> Circular RNAs have a continuous structure and are more stable in vivo than linear RNAs. Recently, transcriptome analysis has revealed the existence of endogenous circular RNAs, some of which have translatable open reading frames. However, the mechanism of how these circular RNAs are translated in the cell is still unclear. We have reported that circular RNAs containing an infinite open reading frame can be efficiently translated to produce proteins in an Escherichia coli cell-free translation system and in living human cells. This translation system is called “rolling circle translation.” In this system, the circular RNA contains a no stop codon and the number of nucleotides composing the RNA is a multiple of three. The mechanism of rolling circle translation not only provides a long-repeating peptide sequence but also enhances the productivity over a given period of time, because the ribosome does not need to bind to the RNA template multiple times, which is the rate limiting step in the reaction cycle. Keywords: Circular RNA / Translation / Rolling Circle Translation |
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| Polymer Science and I: A Personal Account |
| Live by What You Love | Hiroaki IMOTO |
| <Abstract> In today’s world, it is natural to live by what you love. I have wanted to be a chemist since I was a child, and now I am living by what I love. |
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| Front-Line Polymer Science |
| Recent Development in Separation, Purification, and Characterization of Ring Polymers | Atsushi TAKANO |
| <Abstract> Ring polymers is one of the most interesting model polymers especially from the aspect of the polymer dynamics, because they have no chain ends. By the recent development of HPLC techniques with high resolution, highly-purified ring polymers could be prepared, and the understanding of essential physical properties on ring polymers have been progressing. In this article, further developments in separation, purification, and characterization of ring polymers are described. Keywords: Ring Polymer / Separation / Purification / Characterization / Viscoelastic Property |
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