| POLYMERS Vol.65 No.9 |
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COVER STORY
Polymer Synthesis: Tradition, Yet Originality |
| COVER STORY: Highlight Reviews |
| Functional Polymers via Precision Radical Polymerization: Cutting Edge in Primary Structure Control and Self-Assembly | Takaya TERASHIMA, Mitsuo SAWAMOTO |
| <Abstract> This review article presents the cutting edge of the design, synthetic strategies, and self-assembly of functional polymers via living radical polymerization (LRP). Combination of LRP with other polymerizations (or organic reactions) or molecular recognition is effective to produce functional polymers with precision primary structure (e.g., molecular weight, terminal, and monomer sequence): gradient or sequence-controlled copolymers via concurrent tandem LRP with monomer-selective transesterification, telechelic or pinpoint-functionalized polymers via iterative tandem catalysis of LRP and terminal-selective transesterification, and large in-chain ring polymers via cation template-assisted cyclopolymerization. Amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) and hydrophobic alkyl pendants serve as novel self-assembly materials in water, efficiently forming unimer micelles or nanoaggregates. The folding and association properties, i.e., higher-order structure, can be controlled by the primary structure (chain length and composition), much more precisely and conveniently than using block counterparts. Keywords: Functional Polymer / Living Radical Polymerization / Tandem Catalysis / Primary Structure / Sequence Control / Self-Assembly / Folding / Amphiphilic |
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| Monomer Sequence Analysis of Copolymers Obtained by Various Polymer Reactions | Koichi UTE, Tomohiro HIRANO |
| <Abstract> Partial chemical conversion of side groups of homopolymers (e.g. hydrolysis, hydrogenation, transesterification) gives copolymers with various sequence distributions. The other molecular parameters of the homopolymer (e.g. stereoregularity, degree of polymerization) are retained in the resulting copolymers. Thus, polymer reaction is a useful way of controlling monomer sequence of copolymer. Transesterification of poly(vinyl acetate) catalyzed by dilithium tetra(tert-butyl)zincate gives vinyl acetate (VAc) - vinyl alcohol (VOH) copolymers with unusual sequence distributions: 1H NMR spectra of the copolymers showed that the VAc-centered triads distribution is random while that the VOH-centered triads distribution is blocky. Monomer sequence analysis of benzyl methacrylate (BnMA) - methyl methacrylate (MMA) copolymers prepared by various polymer reactions of poly(BnMA) was carried out by multivariate analysis of 13C NMR spectra of the copolymers. The analysis revealed that the copolymers obtained by catalytic hydrogenation of poly(BnMA) are blocky and the copolymers obtained by basic hydrolysis of poly(BnMA) are random-like with a somewhat alternating character. Keywords: NMR Spectroscopy / Multivariate Analysis / Average Sequence Length / Persistence Ratio / Hydrolysis / Catalytic Hydrogenation / Transesterification / Neighboring Group Effect |
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| Recent Progress in Olefin Coordination/ Metathesis Polymerization | Kotohiro NOMURA |
| <Abstract> Selected recent topics concerning synthesis of new polyolefins by incorporation of monomers (disubstituted olefins, sterically encumbered α-olefin etc.), which have never been used by Ziegler-Natta, ordinary metallocenes, and linked half-titanocenes, using designed early transition metal catalysts are introduced. Recent catalyst development also enables synthesis of new highly transparent, thermally resistant cyclic olefin copolymers. Synthesis of polyolefins containing reactive functionality with uniform composition has also been achived by incorporation of nonconjugated diene in ethylene copolymerization, or syndiospecifc styrene polymerization in the presence of p-divinyl benzene etc. Recent catalyst developments for stereo-specific olefin metathesis reactions/polymerizations are also introduced; several examples, which proceed via highly cis-specific olefin metathesis reactions, are introduced. Keywords: New Polyolefins / Complex Catalysts / Coordination Polymerization / Metathesis / ROMP / Cyclic Olefin Copolymers / Titanium / Vanadium |
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| COVER STORY: Topics and Products |
| Precise Synthesis of Substituted Polyacetylenes | Fumio SANDA |
| <Abstract> Substituted polyacetylenes have received considerable attention, owing to their properties resulting from the π-conjugated backbone such as photoconductivity and electroluminescence. The introduction of functional groups at the side chains provides polyacetylenes with useful structural features including liquid crystallinity, molecular recognition, stimuli-responsiveness, and gas permeability. Substituted polyacetylenes are synthesized by the polymerization of the corresponding acetylene monomers using transition-metal catalysts. Rh catalysts bearing a triphenylvinyl group polymerize substituted acetylene monomers in a living fashion to give polymers with controlled molecular weights, geometry and end structures. Pd catalysts bearing bulky phosphine ligands polymerize disubstituted acetylene monomers via the coordination-insertion mechanism. Substituted polyacetylenes bearing chiral substituents adopt helical conformations, whose predominant screw sense transforms between right- and left-handed in CHCl3/MeOH with respect to the solvent composition. The polymers prefer conformations with large dipole moments in polar media, confirmed by the semi empirical molecular orbital calculations, COSMO method. Keywords: Higher Order Structure / Optically Active Polymer / Palladium Catalyst / Polyacetylene / Rhodium Catalyst |
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| New Developments of Pd-Initiated Polymerization of Diazoacetates | Hiroaki SHIMOMOTO, Eiji IHARA |
| <Abstract> Recent developments of Pd-initiated polymerization of diazoacetates are described. Polymerization of diazoacetates is a useful method for preparing C-C main chain polymers bearing an ester substituent on each main chain carbon atom [poly(substituted methylene)s]. However, the substituents introduced into the side chain were limited to hydrophobic groups, and controlled polymerization has not been achieved so far. Recently, we have successfully synthesized poly(substituted methylene)s with hydrophilic groups including hydroxy group and oligo(ethylene glycol) units. The resulting polymers were found to show higher hydrophilicity compared to the corresponding vinyl polymer counterparts. In addition, we have succeeded in controlling the polymerization of diazoacetates for the first time by employing cyclophosphazene-containing diazoacetates as monomers. Keywords: Pd Complex / Diazoacetate / Hydroxy Group / Oligo(ethylene glycol) / LCST-Type Phase Separation / Controlled Polymerization / Cyclotriphosphazene |
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| Elucidating the Mechanism of Polymerization using Synchrotron X-Ray Absorption Spectroscopy | Tomoyasu HIRAI |
| <Abstract> Polymerization of 3-hexylthiophene (3HT) with FeCl3 is simple, efficient, and has been widely adopted for both laboratory and industrial scale production purpose. However, there remains considerable debate regarding the polymerization mechanism. We have used partial fluorescence yield X-ray absorption fine structure (XAFS) techniques to monitor the change in valence state of the solid FeCl3 particles in CHCl3 and hexane. The FeCl3 acts as a catalyst when the reaction is performed in CHCl3, but behaves as an oxidant in hexane. The catalytic behavior is attributed to the decomposition of CHCl3, which has been previously reported to oxidize Fe2+ to Fe3+. This is the first report on the catalytic role of FeCl3 during the polymerization of 3HT in CHCl3. Keywords: Synchrotoron Radiation / Reaction Mechanism / X-Ray Absorption Fine Structure (XAFS) / Catalysts |
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| Polymer Science and I: A Personal Account |
| Keep Multifarious Vibes to Do Creative Study | Kazuhiro SHIKINAKA |
| <Abstract> To do creative studies, I keep it in my mind to experience various things in accordance with ancestors’ wisdom. As a result, I can get “multifarious vibes for various scientific topics”, which will let me experience a rich and fruitful researcher’s life. |
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| Front-Line Polymer Science |
| Synthesis and Applications of Polymers Possessing Extended -Electronic Systems | Ikuyoshi TOMITA, Hiroki NISHIYAMA, Yoshimasa MATSUMURA |
| <Abstract> Recent progress in the synthesis of polymers possessing extended π-electronic systems is reviewed. That is, polymers possessing through space π-electronic interactions and those having π-conjugated systems along the main chain are focused from the viewpoint of polymer synthetic chemistry. Regarding the synthesis of π-conjugated polymers, new methods such as the catalyst-transfer polymerizations, the direct arylation polycondensations, the three-component polycondensations, and the main chain-transformations of the organometallic polymer precursors are described. Some characteristics of the polymers obtained by these methods are also briefly described. Keywords: π-Conjugated Polymers / Polycondensation / Catalyst-Transfer Polymerization / Direct Arylation / Polymer Reaction / Organometallic Polymer |
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