The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Tsutomu Yokozawa - One of the best experts on this subject based on the ideXlab platform.
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chain growth Polycondensation the living polymerization process in Polycondensation
Progress in Polymer Science, 2007Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:Abstract The historical development of research on the living polymerization process in Polycondensation is reviewed. Classical Polycondensation is a step-growth process, but a living polymerization Polycondensation must proceed by a chain-growth rather than a step growth mechanism. Early work demonstrated that some Polycondensations do not obey Flory's statistical treatment: for example, high molecular weight polymer may be obtained, even at low conversion. This means that a chain-growth mechanism must be involved, with or without a step-growth mechanism. Recent years have seen dramatic development in understanding of Polycondensations that proceed only by chain-growth (chain-growth Polycondensation). Several possible mechanisms are: (1) activation of the polymer end group by changed substituent effects between the monomer and the polymer, as with aromatic polyamides, polyesters, polyethers, poly(ether sulfone)s and poly(ether ketone)s; (2) activation of the polymer end group by transfer to it of the catalyst, as with polythiophenes; (3) transfer of the reactive species, derived from the initiator, to the polymer end group, as with polymethylenes and polyphosphazenes; and (4) phase-transfer polymerization in a biphase composed of a monomer storage phase and a polymerization phase, as with aliphatic polyesters. These chain-growth Polycondensations have been applied to the synthesis of condensation polymers with various architectures: block copolymers, star polymers, graft copolymers, etc.
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inductive effect assisted chain growth Polycondensation synthetic development from para to meta substituted aromatic polyamides with low polydispersities
Journal of the American Chemical Society, 2005Co-Authors: Ryuji Sugi, Taniyuki Furuyama, Akihiro Yokoyama, Masanobu Uchiyama, Tsutomu YokozawaAbstract:The Polycondensation of m-(octylamino)benzoic acid esters (1) with base was investigated in order to extend the synthesis of well-defined condensation polymers from para-substituted polymers to meta-substituted ones. We expected that the aminyl anion of 2 would deactivate the ester moiety at the meta position of 2 owing to the strong inductive effect of the anion, resulting in, not self-Polycondensation, but chain-growth Polycondensation. The methyl ester monomer 1a polymerized with lithium hexamethyldisilazide (LiHMDS) in the presence of phenyl benzoate (3a) as an initiator at 0 °C to afford a polymer with a low polydispersity, but the product contained a small amount of self-condensation polymer. On the other hand, the polymerization of the ethyl ester monomer (1b) with phenyl 4-methylbenzoate (3b) proceeded through chain polymerization without self-Polycondensation. The Mn values of the polymers increased linearly in proportion to the [1b]0/[3b]0 ratio, and the Mw/Mn ratios remained narrow over the ent...
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chain growth Polycondensation for well defined condensation polymers and polymer architecture
Chemical Record, 2005Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:The historical development of our research on Polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth Polycondensation") for well-defined condensation polymers is described. We first studied Polycondensation in which change of the substituent effect induced by bond formation drove the reactivity of the polymer end group higher than that of the monomer. In this approach, well-defined aromatic polyamides, polyesters, polyethers, and poly(ether sulfone)s were obtained. The second approach was the study of the phase-transfer polymerization of a solid monomer dispersed in an organic solvent. In this type of polymerization, the solid monomer was physically unable to react with another monomer and was carried with the phase transfer catalyst into the solution phase where it reacted with an initiator and the polymer end group in the solvent in a chain polymerization manner. We also found catalyst-transfer Polycondensation as a third approach to chain-growth Polycondensation. In the Ni-catalyzed Polycondensation of 2-bromo-5-chloromagnesiothiophenes, the Ni catalyst transferred to the polymer end group, and a coupling reaction occurred there to yield a well-defined polythiophene. This chain-growth Polycondensation was applied to the synthesis of condensation polymer architectures such as block copolymers, star polymers, graft copolymers, and so on.
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Chain-Growth Polycondensation: Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture
Polymer Journal, 2004Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:In this review article, Polycondensation that proceeds in a chain-growth polymerization manner (“chain-growth Polycondensation”) for well-defined condensation polymers are described. Our approach to chain-growth Polycondensation is (1) activation of polymer end group by substituent effects changed between monomer and polymer and (2) phase-transfer polymerization in biphase composed of monomer store phase and polymerization phase. In the approach (1), a variety of condensation polymers such as aromatic polyamides, aromatic polyesters, aromatic polyethers, poly(ether sulfone), and polythiophene with defined molecular weights and low polydispersities were obtained. Their Polycondensations had all of the characteristics of living polymerization: a linear correlation between molecular weights and monomer conversion maintaining low polydispersities, and control over molecular weights by the feed ratio of monomer to initiator. Taking advantage of the nature of living polymerization in this Polycondensation, we synthesized diblock copolymers of different kinds of aromatic polyamides and of aromatic polyamide and conventional polymers such as poly(ethylene glycol), polystyrene, and poly(tetrahydrofuran), as well as triblock copolymers and star polymers containing aromatic polyamide units. Some copolymers were arranged in a supramolecular self-assembly. In the approach (2), the Polycondensation of solid monomer dispersed in organic solvent with a phase transfer catalyst (PTC) was carried out, where solid monomer did not react with each other, and the monomer transferred to organic solvent with PTC reacted with an initiator and the polymer end group selectively in organic solvent, to yield well-defined polyesters.
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chain growth Polycondensation for aromatic polyethers with low polydispersities living polymerization nature in Polycondensation
Macromolecules, 2003Co-Authors: Yukimitsu Suzuki, Shuichi Hiraoka, And Akihiro Yokoyama, Tsutomu YokozawaAbstract:Polycondensation normally proceeds in a step-growth reaction manner to give polymers with a wide range of molecular weights. However, the Polycondensation of potassium 5-cyano-4-fluoro-2-propylphenolate (1) proceeded at 150 °C in a chain polymerization manner from an initiator, 4-fluoro-4‘-trifluoromethylbenzophenone (2a), to give aromatic polyethers having controlled molecular weights and low polydispersities (Mw/Mn ≤ 1.1). The resulting Polycondensation of 1 had all of the characteristics of living polymerization and displayed a linear correlation between molecular weight and monomer conversion, maintaining low polydispersities. The MALDI−TOF mass spectrum of poly1 revealed that this Polycondensation did not include conventional step-growth Polycondensation which gave the polymer without initiation unit and macrocycles. The poly1 with low polydispersity showed higher crystallinity than that with broad molecular weight distribution, obtained by the conventional Polycondensation of 1 without 2a.
Akihiro Yokoyama - One of the best experts on this subject based on the ideXlab platform.
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chain growth Polycondensation the living polymerization process in Polycondensation
Progress in Polymer Science, 2007Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:Abstract The historical development of research on the living polymerization process in Polycondensation is reviewed. Classical Polycondensation is a step-growth process, but a living polymerization Polycondensation must proceed by a chain-growth rather than a step growth mechanism. Early work demonstrated that some Polycondensations do not obey Flory's statistical treatment: for example, high molecular weight polymer may be obtained, even at low conversion. This means that a chain-growth mechanism must be involved, with or without a step-growth mechanism. Recent years have seen dramatic development in understanding of Polycondensations that proceed only by chain-growth (chain-growth Polycondensation). Several possible mechanisms are: (1) activation of the polymer end group by changed substituent effects between the monomer and the polymer, as with aromatic polyamides, polyesters, polyethers, poly(ether sulfone)s and poly(ether ketone)s; (2) activation of the polymer end group by transfer to it of the catalyst, as with polythiophenes; (3) transfer of the reactive species, derived from the initiator, to the polymer end group, as with polymethylenes and polyphosphazenes; and (4) phase-transfer polymerization in a biphase composed of a monomer storage phase and a polymerization phase, as with aliphatic polyesters. These chain-growth Polycondensations have been applied to the synthesis of condensation polymers with various architectures: block copolymers, star polymers, graft copolymers, etc.
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inductive effect assisted chain growth Polycondensation synthetic development from para to meta substituted aromatic polyamides with low polydispersities
Journal of the American Chemical Society, 2005Co-Authors: Ryuji Sugi, Taniyuki Furuyama, Akihiro Yokoyama, Masanobu Uchiyama, Tsutomu YokozawaAbstract:The Polycondensation of m-(octylamino)benzoic acid esters (1) with base was investigated in order to extend the synthesis of well-defined condensation polymers from para-substituted polymers to meta-substituted ones. We expected that the aminyl anion of 2 would deactivate the ester moiety at the meta position of 2 owing to the strong inductive effect of the anion, resulting in, not self-Polycondensation, but chain-growth Polycondensation. The methyl ester monomer 1a polymerized with lithium hexamethyldisilazide (LiHMDS) in the presence of phenyl benzoate (3a) as an initiator at 0 °C to afford a polymer with a low polydispersity, but the product contained a small amount of self-condensation polymer. On the other hand, the polymerization of the ethyl ester monomer (1b) with phenyl 4-methylbenzoate (3b) proceeded through chain polymerization without self-Polycondensation. The Mn values of the polymers increased linearly in proportion to the [1b]0/[3b]0 ratio, and the Mw/Mn ratios remained narrow over the ent...
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chain growth Polycondensation for well defined condensation polymers and polymer architecture
Chemical Record, 2005Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:The historical development of our research on Polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth Polycondensation") for well-defined condensation polymers is described. We first studied Polycondensation in which change of the substituent effect induced by bond formation drove the reactivity of the polymer end group higher than that of the monomer. In this approach, well-defined aromatic polyamides, polyesters, polyethers, and poly(ether sulfone)s were obtained. The second approach was the study of the phase-transfer polymerization of a solid monomer dispersed in an organic solvent. In this type of polymerization, the solid monomer was physically unable to react with another monomer and was carried with the phase transfer catalyst into the solution phase where it reacted with an initiator and the polymer end group in the solvent in a chain polymerization manner. We also found catalyst-transfer Polycondensation as a third approach to chain-growth Polycondensation. In the Ni-catalyzed Polycondensation of 2-bromo-5-chloromagnesiothiophenes, the Ni catalyst transferred to the polymer end group, and a coupling reaction occurred there to yield a well-defined polythiophene. This chain-growth Polycondensation was applied to the synthesis of condensation polymer architectures such as block copolymers, star polymers, graft copolymers, and so on.
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Chain-Growth Polycondensation: Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture
Polymer Journal, 2004Co-Authors: Tsutomu Yokozawa, Akihiro YokoyamaAbstract:In this review article, Polycondensation that proceeds in a chain-growth polymerization manner (“chain-growth Polycondensation”) for well-defined condensation polymers are described. Our approach to chain-growth Polycondensation is (1) activation of polymer end group by substituent effects changed between monomer and polymer and (2) phase-transfer polymerization in biphase composed of monomer store phase and polymerization phase. In the approach (1), a variety of condensation polymers such as aromatic polyamides, aromatic polyesters, aromatic polyethers, poly(ether sulfone), and polythiophene with defined molecular weights and low polydispersities were obtained. Their Polycondensations had all of the characteristics of living polymerization: a linear correlation between molecular weights and monomer conversion maintaining low polydispersities, and control over molecular weights by the feed ratio of monomer to initiator. Taking advantage of the nature of living polymerization in this Polycondensation, we synthesized diblock copolymers of different kinds of aromatic polyamides and of aromatic polyamide and conventional polymers such as poly(ethylene glycol), polystyrene, and poly(tetrahydrofuran), as well as triblock copolymers and star polymers containing aromatic polyamide units. Some copolymers were arranged in a supramolecular self-assembly. In the approach (2), the Polycondensation of solid monomer dispersed in organic solvent with a phase transfer catalyst (PTC) was carried out, where solid monomer did not react with each other, and the monomer transferred to organic solvent with PTC reacted with an initiator and the polymer end group selectively in organic solvent, to yield well-defined polyesters.
Yoshiharu Kimura - One of the best experts on this subject based on the ideXlab platform.
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ring opening polymerization of a macrocyclic lactone monomer isolated from oligomeric byproducts of poly butylene succinate pbs an efficient route to high molecular weight pbs and block copolymers of pbs
Polymer, 2014Co-Authors: Kazunari Masutani, Yoshiharu KimuraAbstract:Abstract A macrocyclic lactone (BSD) consisting of butylene succinate dimer was successfully isolated from oligomeric byproducts of poly(butylene succinate) (PBS) prepared by the Polycondensation method. BSD was subjected to ring-opening polymerization (ROP) with tin octoate as the catalyst to obtain PBS. Its number-average molecular weight was found to reach about 9.5 × 10 ４ Da, being much higher than that of the PBS sample obtained by direct melt Polycondensation. When the ROP of BSD was performed in the presence of polyethylene glycol (PEG) as the macro-initiators, triblock (PBS-PEG-PBS) and diblock (PEG-PBS) copolymers were obtained.
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an efficient solid state Polycondensation method for synthesizing stereocomplexed poly lactic acid s with high molecular weight
Journal of Polymer Science Part A, 2008Co-Authors: Kazuki Fukushima, Yoshiharu KimuraAbstract:Simultaneous solid-state Polycondensation (SSP) of the powdery prepolymers of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) can produce entire stereocomplexed poly(lactic acid)s (sc-PLA) with high molecular weight and can be an alternative synthetic route to sc-PLA. Ordinary melt Polycondensations of L- and D-lactic acids gave the PLLA and PDLA prepolymers having medium molecular weight which were pulverized for blending in 1:1 ratio. The resultant powder blends were then subjected to SSP at 130–160 °C for 30 h under a reduced pressure of 0.5 Torr. Some of the products thus obtained attained a molecular weight (Mw) as high as 200 kDa, consisting of stereoblock copolymer of PLLA and PDLA. A small amount of the stereocomplex should be formed in the boundaries of the partially melted PLLA and PDLA where the hetero-chain connection is induced to generate the blocky components. The resultant SSP products showed predominant stereocomplexation after their melt-processing in the presence of the stereoblock components in spite of containing a small amount of racemic sequences in the homo-chiral PLLA and PDLA chains. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3714–3722, 2008
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synthesis of polyglactin by melt solid Polycondensation of glycolic l lactic acids
Polymer International, 2004Co-Authors: Sungil Moo, Kenji Deguchi, Masatoshi Miyamoto, Yoshiharu KimuraAbstract:Polyglactin was successfully synthesized by the melt/solid Polycondensation of a mixture of glycolic acid (GA) and L-lactic acid (LA) mostly at a GA to LA monomer ratio of 90/10. In the polymerization procedure, a solid polycondensate was first prepared by melt-Polycondensation at 150–190 °C, mechanically crushed into particles of various sizes (150–180, 180–210, 210–250, 250–300 and 300–355 µm), and subjected to solid-state post-Polycondensation at 170 °C for 10–20 h. The polyglactin finally obtained was a colourless solid. Catalyst screening revealed that the single use of methanesulfonic acid gave the highest molecular weight of the product. Starting from the crushed melt-polycondensate with a diameter range of 180–250 µm, the highest number-average molecular weight of attained was 80 000 Da. This process can afford a facile route to large-scale synthesis of polyglactin with high molecular weight. Copyright © 2004 Society of Chemical Industry
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melt solid Polycondensation of l lactic acid an alternative route to poly l lactic acid with high molecular weight
Polymer, 2001Co-Authors: S I Moon, C W Lee, Ikuo Taniguchi, M Miyamoto, Yoshiharu KimuraAbstract:Abstract A high polymer of poly( l -lactic acid)(PLLA) is successfully obtained by the melt/solid Polycondensation of l -lactic acid (LA) catalyzed by a tin chloride dihydrate/p-toluenesulfonic acid binary system. In this process, a polycondensate with a molecular weight of 20,000 Da is first prepared by ordinary melt-Polycondensation, crystallized by heat-treatment around 105°C, and heated at 140 or 150°C for 10–30 h for further Polycondensation. A high-quality polymer of PLLA can be obtained in high yield in a relatively short reaction time and its molecular weight exceeds 500,000 Da which is comparable with that of the PLLA obtained by the lactide method but has never been attained by the simple melt-Polycondensation.
Alessandro Gandini - One of the best experts on this subject based on the ideXlab platform.
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thermoreversible nonlinear diels alder polymerization of furan plant oil monomers
Journal of Polymer Science Part A, 2013Co-Authors: Carla Vilela, António Jorge Silvestre, Alessandro GandiniAbstract:Novel trifunctional monomers based on renewable resources were prepared and subsequently polymerized via the Diels-Alder (DA) Polycondensation between furan and maleimide complementary moieties. Three basic approaches were considered for these nonlinear DA Polycondensations, namely the use of (i) a bisfuran monomer in combination with a trismaleimide (A2 + B3 system) and (ii) a trisfuran monomer in conjunction with a bismaleimide (A3 + B2 system) leading to branched or crosslinked materials, and (iii) the use of monomers incorporating both furan and maleimide end groups (A2B or AB2 systems), which lead to hyperbranched structures. The application of the retro-DA reaction to the ensuing polymers confirmed their thermoreversible character. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
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Thermoreversible nonlinear diels-alder polymerization of furan/plant oil monomers
Journal of Polymer Science Part A: Polymer Chemistry, 2013Co-Authors: Carla Vilela, António Jorge Silvestre, Alessandro GandiniAbstract:Novel trifunctional monomers based on renewable resources were prepared and subsequently polymerized via the Diels-Alder (DA) Polycondensation between furan and maleimide complementary moieties. Three basic approaches were considered for these nonlinear DA Polycondensations, namely the use of (i) a bisfuran monomer in combination with a trismaleimide (A2 + B3 system) and (ii) a trisfuran monomer in conjunction with a bismaleimide (A3 + B2 system) leading to branched or crosslinked materials, and (iii) the use of monomers incorporating both furan and maleimide end groups (A2B or AB2 systems), which lead to hyperbranched structures. The application of the retro-DA reaction to the ensuing polymers confirmed their thermoreversible character. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Takaki Kanbara - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of conjugated polymers via direct C–H/C–Cl coupling reactions using a Pd/Cu binary catalytic system
'Royal Society of Chemistry (RSC)', 2019Co-Authors: 桑原 純平, Junpei Kuwabara, 神原 貴樹, Wataru Tsuchida, Shuyang Guo, Takeshi Yasuda, Takaki KanbaraAbstract:Direct arylation Polycondensation is regarded as an efficient synthetic method for conjugated polymers. This methodology is difficult to apply to dichloroaryl monomers because of the low reactivity of the C–Cl bonds compared to that of the C–Br bonds in dibromoaryl monomers, which have been widely used in direct arylation Polycondensation. In this research, direct arylation Polycondensation of dichloroaryl monomers was achieved by the use of a Pd/Cu binary catalytic system. Optimisation of the molar ratio of the Pd and Cu catalyst resulted in the formation of high-molecular-weight polymers in good yields. Structural defects of the polymer at the terminal unit were minimised by logical choice of the monomer ratio on the basis of the reaction mechanism. The obtained polymer with relatively low structural defects showed a higher quantum efficiency of photoluminescence and electroluminescence than that of the polymer with irregular terminal structures
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detailed optimization of Polycondensation reaction via direct c h arylation of ethylenedioxythiophene
Macromolecular Rapid Communications, 2013Co-Authors: Koutarou Yamazaki, Junpei Kuwabara, Takaki KanbaraAbstract:The Polycondensation reaction of 3,4-ethylenedioxythiophene with 2,7-dibromo-9,9-dioctylfluorene via Pd-catalyzed direct arylation gives poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)]. The reaction conditions are optimized in terms of the Pd precatalysts, reaction time, and carboxylic acid additives. The combination of 1 mol% Pd(OAc)(2) and 1-adamantanecarboxylic acid as an additive is the optimized catalytic system, and it yields the corresponding polymer with a molecular weight of 39,400 in 89% yield. The Polycondensation reaction, followed by an end-capping reaction, effectively provides a linear polymer without Br terminals.
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synthesis of thiophene and bithiophene based alternating copolymers via pd catalyzed direct c h arylation
ACS Macro Letters, 2012Co-Authors: Yohei Fujinami, Junpei Kuwabara, Hideki Hayashi, Takaki KanbaraAbstract:Polycondensation via direct C–H arylation of thiophene derivatives gave thiophene- and bithiophene-based alternating copolymers in good yields. The optimization of the reaction conditions was investigated in terms of a catalytic system and reaction time. Under optimized conditions, the Polycondensation reaction of 3,3′,4,4′-tetramethylbithiophene with 2,7-dibromo-9,9-dioctylfluorene gave poly[2,7-(9,9-dioctylfluorene)-alt-5,5′-(3,3′,4,4′-tetramethyl-2,2′-bithiophene)] with a molecular weight of 31 800 in 91% yield. The Polycondensation reaction proceeded with 2 mol % of Pd(OAc)2 without the addition of a phosphine ligand in a short reaction time (3 h). Six kinds of π-conjugated polymers were synthesized by the Polycondensation reaction without the use of bifunctional organometallic reagents as monomers.
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preparation of polythioamides from dialdehydes and diamines with sulfur by the willgerodt kindler type reaction
Journal of Polymer Science Part A, 2001Co-Authors: Takaki Kanbara, Yoritatsu Kawai, Kiyoshi Hasegawa, Hiroyuki Morita, Takakazu YamamotoAbstract:Willgerodt-Kindler type reactions of dialdehydes and diamines in the presence of sulfur were investigated for preparation of polythioamides. The one-pot, three-component Polycondensation afforded various polythioamides in moderate to good yields. The appropriate reaction conditions were examined for the separate monomers. The results led us to the proposed mechanism for the Polycondensation including formation of the intermediate Schiff base polymers followed by the successive nucleophilic attack of polysulfide anions to the azomethine units to give the thioamide groups. Structure, solubility, and thermal properties of the polythioamides were also compared with those of analogous polyamides.
