Li Guojie, Du Peng, Xu Guangqiang, Guo Xuanhua, Wang Qinggang
Key Laboratory of Photoelectric Conversion and Utilization of Solar Energy, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101, China.
Shandong Energy Institute, Qingdao, 266101, China.
Chemistry. 2024 Sep 19;30(53):e202402201. doi: 10.1002/chem.202402201. Epub 2024 Sep 5.
Asymmetric kinetic resolution polymerization (AKRP) provides an ideal way to obtain highly isotactic polylactide (PLA) with superior thermal-mechanical properties from racemic lactide (rac-LA). However, the development of a new catalytic system with concurrent high activity and selectivity at ambient temperature remains a great callenge. Here, a series of simple and effective binary organocatalytic pairs containing axial-chiral thioureas and commercially available phosphazene bases were designed. These chiral binary organocatalytic pairs allow for both high polymerization activity and moderate enantioselectivity for AKRP of rac-LA at room temperature, yielding semi-crystalline and metal-free stereoblock PLA with a melting temperature as high as 186 °C. The highest kinetic resolution coefficient (k) of 8.5 at 47 % conversion was obtained, and D-LA was preferentially polymerized via kinetic resolution with a maximum selectivity factor (k/k) of 18.1, indicating that an enantiomorphic site control mechanism (ESC) was involved.
不对称动力学拆分聚合（AKRP）为从外消旋丙交酯（rac-LA）获得具有优异热机械性能的高度全同立构聚丙交酯（PLA）提供了一种理想方法。然而，开发一种在环境温度下同时具有高活性和选择性的新型催化体系仍然是一个巨大挑战。在此，设计了一系列包含轴手性硫脲和市售磷腈碱的简单有效的二元有机催化对。这些手性二元有机催化对在室温下对rac-LA的AKRP既具有高聚合活性又具有适度的对映选择性，可得到熔点高达186 °C的半结晶且不含金属的立构嵌段PLA。在47 %转化率时获得了最高动力学拆分系数（k）为8.5，并且通过动力学拆分优先聚合D-LA，最大选择性因子（k/k）为18.1，表明涉及对映异构位点控制机制（ESC）。
