新たな開環重合の方法―シクロデキストリンを用いた超分子触媒―

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タイトル別名
  • Novel Ring-Opening Polymerization—Supramolecular Catalysts Using Cyclodextrins—
  • アラタ ナ カイカン ジュウゴウ ノ ホウホウ : シクロデキストリン オ モチイタ チョウブンシ ショクバイ
  • Novel Ring-Opening Polymerization^|^mdash;Supramolecular Catalysts Using Cyclodextrins^|^mdash;

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Cyclodextrins (CDs) initiate ring-opening polymerizations of lactones selectively to give polyesters in high yields. The order of the polymer yield of β-butyrolactone (β-BL) with CDs is α-CD≅β-CD»γ-CD>no CD. On the other hand, that of δ-valerolactone (δ-VL) is β-CD>γ-CD»α-CD>no CD. The yields of the polyesters depend on the cavity size of CDs and structures of lactones, indicating that the reaction took place via inclusion of lactones in the CD cavity. The included monomer in the CD cavity is activated by the formation of hydrogen bonds between the hydroxyl group of CDs and the carbonyl oxygen of monomers in the initiation step. Moreover, CDs threaded onto the polymer are essential for the polymerization propagation step. The polyrotaxane structure prevents the polymer chain from forming random coil conformation. The formation of the polyrotaxane structure keeps the catalytic space of β-CD at the end of polymer. However, an unfixed CD on the polymer chain would leave the active site of β-CD as polymerization proceeds by an insertion of esters between β-CD and the growing chain. To prevent CDs threaded onto the polymer from leaving the active site CD, a molecular clamp CD is covalently bound close to the active β-CD to form the CD dimer. One of CD rings in the dimer functions as the active binding site for the monomer. The other acts as an artificial molecular clamp to grow a higher molecular weight polymer chain. These CD dimers efficiently initiate polymerization to produce polyesters. This behavior is similar to a sliding DNA clamp-clamp loader complex, which plays an important role in propagating DNA in biological systems.

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