The isoselective ring-opening polymerization of racemic lactide was achieved by combining N-heterocyclic olefin (NHO) with mono(thio)ureas or bis(thio)ureas as catalytic systems. The polymerization process shows high stereoselectivity, controllability and reactivity, delivering multi-block isotactic polylactides with high chain-end fidelity and narrow molecular weight distributions. The enhancement of catalytic performance was observed in the following order: bisthiourea (DTU) < monothiourea (TU) < bisurea (DU) < urea (U). The highest P_m (probability of forming a meso dyad) = 0.91 was observed at −70 °C when using NHO/U1 catalytic system and the high stereoselectivity was attributed to chain-end control mechanism.

外消旋丙交酯的等选择性开环聚合反应是通过将N-杂环烯烃（NHO）与单（硫）脲或双（硫）脲作为催化体系结合而实现的。聚合过程显示出高的立体选择性，可控制性和反应性，可提供具有高链端保真度和窄分子量分布的多嵌段等规聚丙交酯。按以下顺序观察到催化性能的增强：双硫脲（DTU）<单硫脲（TU）<双脲（DU）<尿素（U）。使用NHO / U1催化系统时，在-70°C时观察到最高P _m（形成内消旋二元体的可能性）= 0.91，并且高立体选择性归因于链端控制机制。