Highly Active Organocatalysts for Stereoselective Ring-Opening Polymerization of Racemic Lactide at Room Temperature,ACS Macro Letters

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Highly Active Organocatalysts for Stereoselective Ring-Opening Polymerization of Racemic Lactide at Room Temperature
ACS Macro Letters ( IF 5.1 ) Pub Date : 2022-09-14 , DOI: 10.1021/acsmacrolett.2c00425
Yongxin Liu ₁ , Jinbo Zhang ₁ , Xinhui Kou ₁ , Shaofeng Liu ₁ , Zhibo Li _{1,

2}

Affiliation

Although significant advances have been achieved, highly stereocontrolled polymerization using organocatalysts is still a great challenge, such as ring-opening polymerization of racemic lactide (rac-LA) for the synthesis of stereoregular polylactide (PLA). In this context, a series of binary organocatalysts consisting of different phosphazenes (CTPB, C₃N₃-Me-P₃, C₃N₃-Py-P₃, t-BuP₂, and t-BuP₄) and achiral ureas (U1–U6) were applied for the stereocontrolled ROP of rac-LA under mild conditions. It is remarkable that C₃N₃-Py-P₃/U4 with the compatible basicity/acidity showed both high activity (92% conversion within 10 min) and great stereoselectivity (P_m = 0.92) at room temperature (20 °C), and the resultant stereoblock PLA had predictable molar mass, narrow distribution (Đ = 1.07), and high melting temperature (T_m = 190 °C). Interactions involved among phosphazene, urea, and initiator were investigated by an in situ NMR technique. It was found that C₃N₃-Py-P₃ reacted with benzyl alcohol (BnOH) to form a relatively loose ion pair in the presence of U4, which accounted for both high activity and stereoselectivity. Kinetics studies for different LA monomers at 20 °C showed k_obs^–1 (rac-LA) = 0.212 min^–1, k_obs^–1 (D-LA) = 0.311 min^–1, and k_obs^–1 (L-LA) = 0.317 min^–1, indicative of the chain end control mechanism for stereocontrolled ROP.

中文翻译：

用于室温下外消旋丙交酯立体选择性开环聚合的高活性有机催化剂

尽管已经取得了重大进展，但使用有机催化剂进行高度立体控制的聚合仍然是一个巨大的挑战，例如外消旋丙交酯 ( rac -LA) 的开环聚合用于合成有规立构聚丙交酯 (PLA)。在此背景下，一系列由不同磷腈（CTPB、C ₃ N ₃ -Me-P ₃、C ₃ N ₃ -Py-P ₃、t -BuP ₂和t -BuP ₄）和非手性脲组成的二元有机催化剂(U1–U6)在温和条件下应用于rac -LA 的立体控制 ROP。值得注意的是，C ₃碱度/酸度相容的N ₃ -Py-P ₃ /U4在室温 (20 °C) 下表现出高活性（10 分钟内 92% 转化率）和高立体选择性 ( P _m = 0.92)，所得立体嵌段 PLA具有可预测的摩尔质量、窄分布 ( Đ = 1.07) 和高熔化温度 ( T _m = 190 °C)。通过原位核磁共振技术研究了磷腈、尿素和引发剂之间的相互作用。发现C ₃ N ₃ -Py-P ₃在 U4 存在下与苯甲醇 (BnOH) 反应形成相对松散的离子对，具有高活性和立体选择性。不同 LA 单体在 20 °C 下的动力学研究显示k _obs^–1 ( rac -LA) = 0.212 min ^–1，k _obs^–1 ( D -LA) = 0.311 min ^–1和k _obs^–1 ( L -LA ) = 0.317 min ^–1，表示立体控制 ROP 的链端控制机制。

更新日期：2022-09-14

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