Synthesis of Main Chain Chiral Polymer via Asymmetric Radical Cyclocopolymerization using a Chiral Diol as a Template.

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  • Kakuchi Toyoji
    Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University
  • Obata Makoto
    北海道大学大学院工学研究科分子化学専攻
  • Yokota Kazuaki
    北海道大学大学院工学研究科分子化学専攻

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  • キラルジオールをテンプレートとした不斉ラジカル環化共重合における主鎖不斉ポリマーの生成機構
  • キラル ジオール オ テンプレート ト シタ フセイ ラジカルカンカ キョウジュウゴウ ニ オケル シュサ フセイ ポリマー ノ セイセイ キコウ

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The cyclocopolymerization of bis (4-vinylbenzoate) (1) of a chiral diol with styrene has been studied in order to clarify the relationship between chiral template structure and its chirality inductivity. The polymerization was carried out using AIBN as an initiator in dry toluene ([1+styrene] 0 = 0.1 mol·L-1) at 60°C. After removal of the chiral template from the resulting polymer 2, the template-free polymer, i.e., poly [(methyl 4-vinylbenzoate) -co-styrene] (3), showed optical activity, which significantly depended on the chiral template used. When the optically active polymer 3 was obtained, the specific rotations ([α] 435) of the polymer increased with a decrease in the mole fraction of methyl 4-vinylbenzoate unit in the polymer, indicating that the optical activity was attributable to the isolated benzoate diad. According to the exciton chirality method, the CD spectra of polymers 3 indicated that the dextrorotatory polymer 3 had a higher content of (S, S) -racemo benzoate diad over (R, R) -racemo one and the levorotatory polymer 3 was in the reverse situation. The stereoselection was also observed in the radical cyclization using an organotin compounds as a chain transfer reagent. In addition, the stereoisomer distribution of the resulting cyclized unimers indicated that the chiral template inhibited the formation of the unfavorable racemo diad in four possible diads. The calculated heat of formation of cyclized radical by means of semiempirical MO calculation supported the experimental results and gave a model for chirality induction.

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