Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University , Ithaca, New York 14853-1301, United States.
J Am Chem Soc. 2016 Mar 2;138(8):2755-61. doi: 10.1021/jacs.5b12888. Epub 2016 Feb 17.
The synthesis of well-defined and functionalizable aliphatic polyesters remains a key challenge in the advancement of emerging drug delivery and self-assembly technologies. Herein, we investigate the factors that influence the rates of undesirable transesterification and epimerization side reactions at high conversion in the copolymerization of tricyclic anhydrides with excess propylene oxide using aluminum salen catalysts. The structure of the tricyclic anhydride, the molar ratio of the aluminum catalyst to the nucleophilic cocatalyst, and the Lewis acidity of the aluminum catalyst all influence the rates of these side reactions. Optimal catalytic activity and selectivity against these side reactions requires a careful balance of all these factors. Effective suppression of undesirable transesterification and epimerization was achieved even with sterically unhindered monomers using a fluorinated aluminum salph complex with a substoichiometric amount of a nucleophilic cocatalyst. This process can be used to synthesize well-defined block copolymers via a sequential addition strategy.
合成具有明确结构和官能团的脂肪族聚酯仍然是新兴药物输送和自组装技术发展的关键挑战。在此，我们研究了在使用铝水杨醛催化剂时，在高转化率下，三环酸酐与过量环氧丙烷共聚时，影响不良酯交换和差向异构化副反应速率的因素。三环酸酐的结构、铝催化剂与亲核助催化剂的摩尔比以及铝催化剂的路易斯酸度都会影响这些副反应的速率。需要仔细平衡所有这些因素，才能获得最佳的催化活性和对这些副反应的选择性。即使使用空间位阻较小的单体，通过使用具有亚化学计量的亲核助催化剂的氟化铝水杨醛配合物，也可以有效地抑制不良的酯交换和差向异构化。通过顺序添加策略，可以使用该方法合成具有明确结构的嵌段共聚物。
