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Akira Hirao - One of the best experts on this subject based on the ideXlab platform.

  • successive synthesis of well defined star branched polymers by a new iterative approach involving coupling and transformation reactions
    Macromolecules, 2005
    Co-Authors: Tomoya Higashihara, Naoki Haraguchi, Masato Nagura, Kyoichi Inoue, Akira Hirao
    Abstract:

    Successive synthesis of well-defined star-branched polymers has been successfully achieved by a new iterative methodology based on living anionic polymerization. The methodology involves only two sets of reaction conditions for the entire iterative reaction sequence: (a) a coupling reaction of the Benzyl Bromide-functionalized polymer with poly(substituted styryl)lithium end-capped with 1-(3-tert-butyldimethylsilyloxymethylphenyl)-1-phenylethylene to link two polymer chains and introduce 3-tert-butyldimethylsilyoxymethylphenyl group(s) of Benzyl Bromide precursor(s) and (b) a transformation reaction of the introduced precursor(s) into Benzyl Bromide functionality (functionalities) by treatment with (CH3)3SiCl−LiBr. By repeating these two reactions, an array of asymmetric star-branched polymers were successively synthesized. They involved 3-arm ABC, 4-arm ABCD and A2B2, and 6-arm A2B2C2 stars whose A, B, C, and D segments are polystyrene, poly(α-methylstyrene), poly(4-methylstyrene), poly(methyl methacryla...

  • precise synthesis of asymmetric star shaped polymers by coupling reactions of new specially designed polymer anions with chain end functionalized polystyrenes with Benzyl Bromide moieties
    Science and Technology of Advanced Materials, 2004
    Co-Authors: Akira Hirao, Kaori Kawasaki, Tomoya Higashihara
    Abstract:

    We have developed a novel methodology using polymer anions specially designed to comprise either of the three same or different polymer segments for the synthesis of well-defined regular and asymmetric star-shaped polymers. The polymer anion was prepared by the addition reaction of living anionic polymer to in-chain-functionalized polymer with 1,1-diphenylethylene (DPE) moiety and in situ coupled with chain-end-functionalized polystyrene with two or four Benzyl Bromide moieties. Although the anions located at the cores of 3-armed star polymers were believed to be highly sterically hindered, the coupling reactions proceeded virtually quantitatively under the conditions in THF at −78 °C for 24 h. Regular 7-armed A7 and 13-armed A13 star-shaped polystyrenes as well as quite new asymmetric 7-armed A2B2C2D and 13-armed A4B4C4D star-shaped polymers were synthesized in ca. 100% yields. Four polymer segments, A, B, C, and D, were, poly(4-trimethylsilylstyrene), poly(4-methoxystyrene), poly(4-methylstyrene), and polystyrene prepared by sec-BuLi-initiated living anionic polymerization. Thus, three same or different polymer chains could be simultaneously introduced into either two or four Benzyl Bromide reaction sites only by one-step coupling reaction with the above-prepared polymer anion. The resulting star-shaped polymers all were well-defined in architecture and precisely controlled in-chain length and composition. Accordingly, they have a high molecular weight and structural homogeneity. Among them, asymmetric star-shaped polymers synthesized herein are the first successful examples comprised of four plural different polymer segments. As expected, new morphologies with nanoscopic ordered structures applicable to nanotechnology have been expressed.

  • synthesis of well defined dendrimer like branched polymers and block copolymer by the iterative approach involving coupling reaction of living anionic polymer and functionalization
    Macromolecules, 2004
    Co-Authors: Akira Matsuo, Takumi Watanabe, Akira Hirao
    Abstract:

    The first-, second-, and third-generation dendrimer-like branched poly(methyl methacrylate)s (PMMA)s were synthesized by an iterative divergent approach which involves a coupling reaction of α-functionalized living anionic PMMA with chain-end-functionalized PMMA with Benzyl Bromide moieties and a transformation reaction of the tert-butyldimethylsilyloxymethylpheny groups into Benzyl Bromide functionalities. The iterative reaction sequence could be repeated three times without problem to afford a series of three generations dendrimer-like branched PMMAs with well-defined architectures and precisely controlled chain lengths. Moreover, an amphiphilic dendrimer-like branched block copolymer was synthesized successfully in a similar manner by using the living anionic polymer of the protected 2-hydroxyethyl methacrylate (HEMA) instead of living anionic PMMA at the final reaction stage. The resulting polymer was made of the inner 1, 4, and 8 PMMA segments and the outer 16 poly(HEMA) segments. The solution behavi...

  • synthesis of chain end functionalized poly methyl methacrylate s with a definite number of Benzyl Bromide moieties and their application to star branched polymers
    Macromolecules, 2003
    Co-Authors: Akira Hirao, Akira Matsuo
    Abstract:

    The synthesis of well-defined chain-end-functionalized poly(methyl methacrylate)s with a definite number of Benzyl Bromide moieties via an iterative divergent approach starting from the living anionic polymer of methyl methacrylate is described. Only two sets of reactions involving coupling and transformation reactions are needed for the entire iterative reaction sequence. By repeating the iterative reaction sequence, chain-end-functionalized poly(methyl methacrylate)s with 2, 4, 8, and 16 Benzyl Bromide moieties were synthesized successfully. The resulting Benzyl Bromide-functionalized poly(methyl methacrylate)s underwent coupling reaction with living anionic polymers of methyl methacrylate, tert-butyl methacrylate, styrene, and isoprene to quantitatively afford well-defined regular 3-, 5-, 9-, and 17-arm star-branched poly(methyl methacrylate)s and asymmetric star-branched polymers containing poly(methyl methacrylate) segments.

  • synthesis of well defined star linear block polystyrenes by coupling reaction of chain functionalized polystyrenes with a definite number of Benzyl Bromide moieties with polystyryllithiums
    Macromolecules, 2003
    Co-Authors: Naoki Haraguchi, Akira Hirao
    Abstract:

    The synthesis of specially designed chain-functionalized polystyrenes with a definite number of Benzyl Bromide moieties by an iterative divergent methodology is described. Such functionalized polystyrenes involve α,ω-chain-end-functionalized polystyrenes with Benzyl Bromide moieties, in-chain-functionalized polystyrenes with Benzyl Bromide moieties, and in-chain-functionalized polystyrenes with Benzyl Bromide moieties that are placed at two sites in a chain. The number of Benzyl Bromide moieties varied from 2 to 16 at each place. Three series of well-defined star−linear block polystyrenes of the types star-block-linear-block-star, linear-block-star-block-linear, and linear-block-star-block-linear-block-star-block-linear have been successfully synthesized by coupling these Benzyl Bromide-chain-functionalized polystyrenes with polystyryllithiums end-capped with 1,1-diphenylethylene.

Naoki Haraguchi - One of the best experts on this subject based on the ideXlab platform.

M W Anders - One of the best experts on this subject based on the ideXlab platform.

  • reactive intermediate formation from the 2 fluoromethoxy 1 1 3 3 3 pentafluoro 1 propene compound a derived cysteine s conjugate s 2 fluoromethoxy 1 1 3 3 3 pentafluoropropyl l cysteine in pyridoxal model systems
    Chemical Research in Toxicology, 2002
    Co-Authors: Zeen Tong, M W Anders
    Abstract:

    2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is a degradation product of the anesthetic sevoflurane and undergoes cysteine conjugate β-lyase-dependent bioactivation to nephrotoxic metabolites in rats. The present experiments were designed to identify reactive intermediates formed from S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine, a compound A-derived cysteine S-conjugate, in two pyridoxal model systems, namely Cu 2 + / pyridoxal and N-dodecylpyridoxalin cetyltrimethylammonium micelles. S-[2-(Fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine was incubated in the model systems with Benzyl Bromide, pentafluoroBenzyl Bromide, aniline, and o-phenylenediamine as trapping agents. The products were purified by TLC and identified by 1 9 F and 1 H NMR spectroscopy and by GC/MS. In the absence of trapping agents, 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid and 3,3,3-trifluorolactic acid, which have been identified previously in biotransformation studies, were formed. With the chemical models, 2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropanethiolate, the expected first intermediate, was not trapped with Benzyl Bromide. Rather, the dehydrofluorination product 2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenylthiolate was trapped with Benzyl Bromide to give Benzyl 2-(fluoromethoxy)-3,3,3-trifluoropropanethioate, which was formed in both chemical models. When pentafluoroBenzyl Bromide was used as a trapping agent, GC/ MS analysis showed that the expected thiolate was trapped to give pentafluoroBenzyl 2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl sulfide in the N-dodecylpyridoxal model. In both chemical models, 2-(fluoromethoxy)-3,3,3-trifluorothioacyl fluoride was trapped with aniline to give N-phenyl 2-(fluoromethoxyl)-3,3,3-trifluoropropanethioamide, which cyclized to give 3-phenyl-4-thiono-5-(trifluoromethyl)-1,3-oxazolane. The results demonstrate that most of the reactive intermediates and products formed by the β-lyase-catalyzed biotransformation of compound A-derived cysteine S-conjugates are also formed in the two chemical systems studied. Some products were, however, formed in chemical systems that have not been observed in previous in vivo and in vitro studies; it is not known whether these products are formed in biological systems and whether they contribute to the observed nephrotoxicity of cysteine S-conjugates.

Tomoya Higashihara - One of the best experts on this subject based on the ideXlab platform.

  • successive synthesis of well defined star branched polymers by a new iterative approach involving coupling and transformation reactions
    Macromolecules, 2005
    Co-Authors: Tomoya Higashihara, Naoki Haraguchi, Masato Nagura, Kyoichi Inoue, Akira Hirao
    Abstract:

    Successive synthesis of well-defined star-branched polymers has been successfully achieved by a new iterative methodology based on living anionic polymerization. The methodology involves only two sets of reaction conditions for the entire iterative reaction sequence: (a) a coupling reaction of the Benzyl Bromide-functionalized polymer with poly(substituted styryl)lithium end-capped with 1-(3-tert-butyldimethylsilyloxymethylphenyl)-1-phenylethylene to link two polymer chains and introduce 3-tert-butyldimethylsilyoxymethylphenyl group(s) of Benzyl Bromide precursor(s) and (b) a transformation reaction of the introduced precursor(s) into Benzyl Bromide functionality (functionalities) by treatment with (CH3)3SiCl−LiBr. By repeating these two reactions, an array of asymmetric star-branched polymers were successively synthesized. They involved 3-arm ABC, 4-arm ABCD and A2B2, and 6-arm A2B2C2 stars whose A, B, C, and D segments are polystyrene, poly(α-methylstyrene), poly(4-methylstyrene), poly(methyl methacryla...

  • precise synthesis of asymmetric star shaped polymers by coupling reactions of new specially designed polymer anions with chain end functionalized polystyrenes with Benzyl Bromide moieties
    Science and Technology of Advanced Materials, 2004
    Co-Authors: Akira Hirao, Kaori Kawasaki, Tomoya Higashihara
    Abstract:

    We have developed a novel methodology using polymer anions specially designed to comprise either of the three same or different polymer segments for the synthesis of well-defined regular and asymmetric star-shaped polymers. The polymer anion was prepared by the addition reaction of living anionic polymer to in-chain-functionalized polymer with 1,1-diphenylethylene (DPE) moiety and in situ coupled with chain-end-functionalized polystyrene with two or four Benzyl Bromide moieties. Although the anions located at the cores of 3-armed star polymers were believed to be highly sterically hindered, the coupling reactions proceeded virtually quantitatively under the conditions in THF at −78 °C for 24 h. Regular 7-armed A7 and 13-armed A13 star-shaped polystyrenes as well as quite new asymmetric 7-armed A2B2C2D and 13-armed A4B4C4D star-shaped polymers were synthesized in ca. 100% yields. Four polymer segments, A, B, C, and D, were, poly(4-trimethylsilylstyrene), poly(4-methoxystyrene), poly(4-methylstyrene), and polystyrene prepared by sec-BuLi-initiated living anionic polymerization. Thus, three same or different polymer chains could be simultaneously introduced into either two or four Benzyl Bromide reaction sites only by one-step coupling reaction with the above-prepared polymer anion. The resulting star-shaped polymers all were well-defined in architecture and precisely controlled in-chain length and composition. Accordingly, they have a high molecular weight and structural homogeneity. Among them, asymmetric star-shaped polymers synthesized herein are the first successful examples comprised of four plural different polymer segments. As expected, new morphologies with nanoscopic ordered structures applicable to nanotechnology have been expressed.

Akira Matsuo - One of the best experts on this subject based on the ideXlab platform.

  • synthesis of well defined dendrimer like branched polymers and block copolymer by the iterative approach involving coupling reaction of living anionic polymer and functionalization
    Macromolecules, 2004
    Co-Authors: Akira Matsuo, Takumi Watanabe, Akira Hirao
    Abstract:

    The first-, second-, and third-generation dendrimer-like branched poly(methyl methacrylate)s (PMMA)s were synthesized by an iterative divergent approach which involves a coupling reaction of α-functionalized living anionic PMMA with chain-end-functionalized PMMA with Benzyl Bromide moieties and a transformation reaction of the tert-butyldimethylsilyloxymethylpheny groups into Benzyl Bromide functionalities. The iterative reaction sequence could be repeated three times without problem to afford a series of three generations dendrimer-like branched PMMAs with well-defined architectures and precisely controlled chain lengths. Moreover, an amphiphilic dendrimer-like branched block copolymer was synthesized successfully in a similar manner by using the living anionic polymer of the protected 2-hydroxyethyl methacrylate (HEMA) instead of living anionic PMMA at the final reaction stage. The resulting polymer was made of the inner 1, 4, and 8 PMMA segments and the outer 16 poly(HEMA) segments. The solution behavi...

  • synthesis of chain end functionalized poly methyl methacrylate s with a definite number of Benzyl Bromide moieties and their application to star branched polymers
    Macromolecules, 2003
    Co-Authors: Akira Hirao, Akira Matsuo
    Abstract:

    The synthesis of well-defined chain-end-functionalized poly(methyl methacrylate)s with a definite number of Benzyl Bromide moieties via an iterative divergent approach starting from the living anionic polymer of methyl methacrylate is described. Only two sets of reactions involving coupling and transformation reactions are needed for the entire iterative reaction sequence. By repeating the iterative reaction sequence, chain-end-functionalized poly(methyl methacrylate)s with 2, 4, 8, and 16 Benzyl Bromide moieties were synthesized successfully. The resulting Benzyl Bromide-functionalized poly(methyl methacrylate)s underwent coupling reaction with living anionic polymers of methyl methacrylate, tert-butyl methacrylate, styrene, and isoprene to quantitatively afford well-defined regular 3-, 5-, 9-, and 17-arm star-branched poly(methyl methacrylate)s and asymmetric star-branched polymers containing poly(methyl methacrylate) segments.