羟基化合物存在下醇铁催化丙交酯开环聚合机理研究

以乙醇铁、正丁醇铁为催化剂,研究了在丙交酯/醇铁的聚合体系中引入羟基化合物催化丙交酯开环聚合的机理。羟基化合物为苄醇时,聚合产物分子是以苄氧基和乳酰基为端基的聚乳酸(PLA),聚合产物的分子量受丙交酯/苄醇摩尔投料比控制;当羟基化合物为聚乙二醇(PEG)时,聚合产物的分子结构为PLA-PEG-PLA的三嵌段共聚物,分子链的端基结构均为乳酰基结构单元,聚合产物的LA/PEG摩尔比与投料比基本一致,醇铁在其中起促进PEG参与聚合成酯的作用。这些结果表明在含羟基化合物的丙交酯/醇铁聚合体系中,羟基化合物作为共引发剂参与了丙交酯的开环聚合。在聚合过程中,羟基化合物首先与醇铁作用形成一种复合物,在这种复合物作用下,丙交酯的酰氧键断裂,按配位-插入机理进行增长。

Mechanism of Ferric Alkoxides Catalyzed Polymerization of Lactide in the Presence of Hydroxyl Compounds

The ring-opening polymerization mechanism of lactide in the presence of hydroxyl compounds was studied by using ferric ethoxide and ferric n-butoxide as catalysts respectively.()~1H NMR analysis showed that polylactide(PLA) with benzyloxy and lactyl end groups was produced when benzyl alcohol was introduced into the lactide/alkoxide polymerization system.The molecular weight of the product depended on the molar ratio of lactide/benzyl alcohol.In the presence of polyethylene glycol(PEG) for the lactide/alkoxide systems,a triblock copolymer PLA-PEG-PLA with lactyl end groups was obtained and the molar ratio of lactide/PEG of the copolymer was basically agreed with the results calculated according to the feed molar ratio.The ferric alkoxides promoted PEG participating in the ring-opening polymerization of lactide and esterification.According to the above results,it was suggested that the hydroxyl compounds acted as co-initiators in the ferric alkoxide/lactide polymerization system.In the polymerization process they first formed complexes with ferric alkoxides,which attacked the lactide carbonyl carbon and the acyl-oxygen bond cleaved because of its being weakened and then the ring-opening polymerization of lactide proceeded via a coordination-insertion mechanism.