Polymerization of lactones and lactides initiated by cyclodextrins
Polymerization of lactones and lactides initiated by cyclodextrins
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DOI：
10.1295/koron.64.607
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发表时间：
2007-01-01
影响因子：
--
通讯作者：
Harada, Akira
中科院分区：
文献类型：
--
作者：
Osaki, Motofumi;Takashima, Yoshinori;Harada, Akira
人们发现环糊精（CD）可以选择性地引发内酯和丙交酯的开环聚合，从而以高产率产生聚酯。具有CD的β-丁内酯的聚合物产率的顺序是α-CD与β-CD>>γ-CD>无CD，而δ-戊内酯(δ-VL)的聚合物产率的顺序是β-CD>α-CD>>γ-CD>无CD。聚酯的产率取决于环糊精的空腔尺寸和内酯的结构，表明反应是通过在环糊精空腔中包含内酯而发生的。 β-CD-金刚烷包合络合物在相同条件下没有表现出任何对δ-VL的聚合活性，因为金刚烷强烈抑制β-CD和δ-VL之间的包合络合物的形成。通过FT-IR光谱观察到，CD空腔中包含的单体在引发步骤中通过CD的羟基与单体的羰基氧之间形成氢键而被激活。发现产物是通过酯键连接到CD的单个吡喃葡萄糖单元的C-2-羟基上的聚合物链。内酯被其他剩余的仲羟基活化，通过在 CD 和聚合物链之间插入单体来提供增长步骤。通过固态 C-13 NMR 技术观察了 CD 引发内酯聚合的引发和增长步骤。
Cyclodextrins (CDs) were found to initiate ring-opening polymerizations of lactones and lactides selectively to give polyesters in high yields. The order of the polymer yield of beta-butyrolactone with CDs is alpha-CD congruent to beta-CD >>gamma-CD > no CD, while the order of the polymer yield of delta-valerolactone (delta-VL) is beta-CD >alpha-CD >>gamma-CD > no CD. The yields of the polyesters depend on the cavity size of CDs and on the structures of lactones, indicating that the reaction took place via inclusion of lactones in the CD cavity. The beta-CD-adamantane inclusion complex did not show any polymerization activity for delta-VL under the same conditions because adamantane strongly inhibits the formation of the inclusion complex between,beta-CD and delta-VL. 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, which was observed by FT-IR spectroscopy. The products were found to be a polymer chain attached to the C-2-hydroxyl group of a single glucopyranose unit of CD via an ester bond. The lactones are activated by the other remaining secondary hydroxyl groups to give the propagation step by way of insertions of monomers between CD and the polymer chain. The initiation and the propagation steps of the polymerization of lactones by CDs were observed by solid state C-13 NMR techniques.