Synergetic Organocatalysis for Eliminating Epimerization in Ring-Opening Polymerizations Enables Synthesis of Stereoregular Isotactic Polyester
作者:Maosheng Li、Yue Tao、Jiadong Tang、Yanchao Wang、Xiaoyong Zhang、Youhua Tao、Xianhong Wang
DOI:10.1021/jacs.8b09739
日期:2019.1.9
ring-opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields
O-羧酸酐 (OCA) 的开环聚合可为聚酯提供多种官能团,而传统上这些官能团很难通过内酯聚合获得。典型的开环催化剂不可避免地会发生大多数 OCA 单体的外消旋化,这阻碍了高度等规结晶聚合物的合成。在这里,我们描述了一种有效的双功能单分子有机催化,用于无差向异构化的 OCA 选择性开环聚合。同一分子中两个活化基团的紧密相邻会产生放大的协同效应,从而允许使用温和的碱,从而使聚合的差向异构化最小化。由双功能单分子有机催化剂介导的 manOCA 单体(来自扁桃酸的 OCA)的开环聚合产生高度全同立构的聚(扁桃酸)(PMA),其分子量受控(高达 19.8 kg mol-1)。PMA 的两种对映异构体的混合在该区域产生了结晶立体复合物的第一个例子,它在 150 °C 左右显示出不同的 Tm 值。值得注意的是,双功能催化剂具有防潮、可回收和易于使用的特点,允许可持续和可扩展地合成有规立构功能聚酯。
Alternating Sequence Controlled Copolymer Synthesis of α-Hydroxy Acids via Syndioselective Ring-Opening Polymerization of <i>O</i>-Carboxyanhydrides Using Zirconium/Hafnium Alkoxide Initiators
challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and
The ring-openingpolymerization of l-lactic acid O-carboxyanhydrides was initiated by triisopropoxyneodymium in toluene-THF mixtures. Typically, high yields and relatively high molecular weight PLAs were obtained within 4 h at 25 °C. The reaction was highly controllable and easy to conduct, and the molecular weight distribution of the PLAs was rather narrow (Mw/Mn = 1.10–1.36). NMR analysis showed
Optically active 3-substituted 2, 3-dihydro-1, 3, 4-thiadiazoles (2-5) were synthesized by the reaction of aldehyde methylthio(thiocarbonyl)hydrazones (1) and chiral 5-substituted 1, 3-dioxolane-2, 4-diones. The absolute configurations of compounds 2-5 were deduced from their circular dichroism spectra.
An Activated Equivalent of Lactide toward Organocatalytic Ring-Opening Polymerization
作者:Olivier Thillaye du Boullay、Emmanuel Marchal、Blanca Martin-Vaca、Fernando P. Cossío、Didier Bourissou
DOI:10.1021/ja067046y
日期:2006.12.1
The alpha-lactone equivalent lacOCA exhibits remarkable reactivity compared with lactide in nucleophile-catalyzed ROP. PLAs of controlled molecular weights and narrow polydispersities are typically obtained under mild conditions using DMAP and various protic initiators.