Liu Shaofeng, Li Huaike, Zhao Na, Li Zhibo
Key Laboratory of Biobased Polymer Materials, Shandong Provincial Education Department; School of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China.
ACS Macro Lett. 2018 Jun 19;7(6):624-628. doi: 10.1021/acsmacrolett.8b00353. Epub 2018 May 16.
Phosphazene base is an important organocatalyst in polymer chemistry owing to its high activity and versatility. In this contribution, we demonstrate that cyclic trimeric phosphazene base () can catalyze stereoselective ring-opening polymerization (ROP) of -lactide (-LA) to produce isotactic stereoblock PLA ( up to 0.93). The polymerizations are highly controlled, as evidenced by linear relationship between molecular weights (MW) and monomer conversions and the narrow dispersity ( = /) of the resulted polymers with high fidelity of end groups. The investigations on polymerization parameters show that the tacticity of produced PLA depends on the polymerization temperatures and solvents, while the kinetic studies reveal a faster rate for ROP of l-LA as compared to -LA under same conditions. Based on these results, the chain end control mechanism is proposed to explain the production of isotactic stereoblock PLA from -LA by an achiral catalyst.
磷腈碱由于其高活性和多功能性，是高分子化学中一种重要的有机催化剂。在本论文中，我们证明了环状三聚磷腈碱（）能够催化丙交酯（-LA）的立体选择性开环聚合（ROP），以制备全同立构嵌段聚乳酸（全同立构规整度高达0.93）。聚合反应具有高度可控性，这体现在分子量（MW）与单体转化率之间的线性关系以及所得聚合物的窄分散度（= /）和高保真端基上。对聚合参数的研究表明，所制备聚乳酸的立构规整度取决于聚合温度和溶剂，而动力学研究表明，在相同条件下，L-LA的ROP速率比-D-LA更快。基于这些结果，我们提出了链端控制机制，以解释由非手性催化剂从-D-LA制备全同立构嵌段聚乳酸的过程。
