Mechanism of the Polymerization of <i>rac</i>-Lactide by Fast Zinc Alkoxide Catalysts
作者:Daniel E. Stasiw、Anna M. Luke、Tomer Rosen、Aaron B. League、Mukunda Mandal、Benjamin D. Neisen、Christopher J. Cramer、Moshe Kol、William B. Tolman
DOI:10.1021/acs.inorgchem.7b02544
日期:2017.11.20
of the ligand framework influences polymerization rate, selectivity, and control. After determination that zinc-ethyl precatalysts required 24 h of reaction with benzyl alcohol to convert to active alkoxide complexes, the subsequently formed species proved to be active and fairly selective, polymerizing up to 300 equiv of rac-LA in 6–10 min while yielding isotactic (Pm = 0.72–0.78) polylactide (PLA)
使用L X Zn催化剂(L X =在结合的酚盐供体上具有可变对位取代基X的酚盐,胺和吡啶供体的配体)进行rac-丙交酯(rac -LA)的开环酯交换聚合(ROTEP)2,Br,t-Bu,OMe)是通过动力学实验和密度泛函理论进行评估的,目的是确定配体骨架的电子调节如何影响聚合速率,选择性和控制力。在确定锌-乙基预催化剂需要与苄醇反应24小时才能转化为活性醇盐络合物后,随后形成的物质被证明具有活性和相当的选择性,可在6-10分钟内聚合多达300当量的rac- LA,同时产生低分散度的等规(P m = 0.72-0.78)聚丙交酯(PLA):Đ = 1.06-1.17。与以前的铝催化剂工作相比,铝催化剂的配体取代基的电子效应显着(Hammettρ= + 1.2-1.4),与之相反,L X锌系统表现出的影响要小得多(ρ= +0.3)。密度泛函计算揭示了引发和传播步骤的细节,从而使人们能够深入了解X的同一性和速率的不敏感性。