Abstract Phosphazenes have attracted considerable attention in the field of ring-opening polymerization (ROP) of cyclic esters. However, the application of phosphazenes as catalyst is subject to a trade-off between activity and selectivity (chain propagation versus transesterification/back-biting reaction, e.g., controlled polymerization). Despite extensive research efforts, the development of a new catalytic system having concurrent high activity and selectivity remains a great challenge. In this work, we report that the binary organocatalytic system comprised of cyclic trimeric phosphazene base (CTPB) and ureas shows both of high activity and selectivity for the ROP of e-caprolactone (e-CL) and δ-valerolactone (δ-VL) in the presence of alcohol as initiator. It is found that the introduction of ureas would significantly increase the catalytic selectivity during ROP without sacrificing the catalytic activity of CTPB. Moreover, the polymerizations catalyzed by the title catalytic system exhibit immortal characteristics and thus thousands equivalent of monomer could be converted to polymer efficiently with desired MWs and microstructures. Linear diblock copolymer AB and star copolymers (AB)3 with three identical diblock arms could be readily synthesized by sequential copolymerization using different alcohols as initiators.

中文翻译：

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ε-己内酯和δ-戊内酯开环聚合的二元有机催化体系：增强选择性的协同效应

摘要 磷腈在环酯的开环聚合（ROP）领域引起了广泛关注。然而，磷腈作为催化剂的应用需要在活性和选择性之间进行权衡（链增长对酯交换/反咬合反应，例如受控聚合）。尽管进行了广泛的研究，但同时具有高活性和选择性的新催化体系的开发仍然是一个巨大的挑战。在这项工作中，我们报告了由环状三聚磷腈碱（CTPB）和尿素组成的二元有机催化系统对ε-己内酯（e-CL）和δ-戊内酯（δ-VL）的ROP显示出高活性和选择性在醇作为引发剂存在下。结果发现，尿素的引入将显着提高 ROP 过程中的催化选择性，而不会牺牲 CTPB 的催化活性。此外，由标题催化体系催化的聚合反应具有不朽的特性，因此数千当量的单体可以有效地转化为具有所需 MW 和微观结构的聚合物。线性二嵌段共聚物 AB 和具有三个相同二嵌段臂的星形共聚物 (AB)3 可以很容易地通过使用不同醇作为引发剂的顺序共聚来合成。由标题催化系统催化的聚合反应具有不朽的特性，因此数千当量的单体可以有效地转化为具有所需 MW 和微观结构的聚合物。线性二嵌段共聚物 AB 和具有三个相同二嵌段臂的星形共聚物 (AB)3 可以很容易地通过使用不同醇作为引发剂的顺序共聚来合成。由标题催化系统催化的聚合反应具有不朽的特性，因此数千当量的单体可以有效地转化为具有所需 MW 和微观结构的聚合物。线性二嵌段共聚物 AB 和具有三个相同二嵌段臂的星形共聚物 (AB)3 可以很容易地通过使用不同醇作为引发剂的顺序共聚来合成。