Zhang Xiangyi, Waymouth Robert M
Department of Chemistry, Stanford University, Stanford, California 94305-5080, United States.
ACS Macro Lett. 2014 Oct 21;3(10):1024-1028. doi: 10.1021/mz500525n. Epub 2014 Sep 23.
Bicyclic isothioureas and mediate controlled ring opening polymerizations (ROP) of lactides in the absence of protic initiators to afford high molecular weight polylactides (PLA) with narrow polydispersities. The cyclic structure of the resulting PLA was determined by dilute solution viscosity measurement and MALDI-TOF mass spectrometry. Compared to DBU initiator, isothioureas are more selective for producing cyclic PLA without appreciable linear contaminants. Mechanistic studies involving acyl amidinium support our hypothesis that DBU-initiated ZROP generates linear chains from a ketene aminal intermediate.
双环异硫脲在无质子引发剂的情况下介导丙交酯的可控开环聚合（ROP），以得到具有窄多分散性的高分子量聚丙交酯（PLA）。通过稀溶液粘度测量和基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）确定所得PLA的环状结构。与1,8-二氮杂双环[5.4.0]十一碳-7-烯（DBU）引发剂相比，异硫脲在生产环状PLA时更具选择性，且几乎没有明显的线性杂质。涉及酰基脒鎓的机理研究支持了我们的假设，即DBU引发的活性环开环聚合（ZROP）从烯酮缩醛中间体生成线性链。
