Synthesis Of Rare Earth Metal Complexes And Their Catalytic Activity For Lactide Polymerization

The petroleum-based polymers are facing a hard problem as the exhausted of oil. And the hardness of degradation of the polymers causes the increased environment pollution problem. So the development of polymer materials will be faced with two problems:raw materials crisis and environment pollution. Accordingly, research and develop environment-friendly, biogradable new materials will be the trend in the future.Polylactide(PLA) is considered as the most promising new "ecological material" as its biodegradable, non-toxic to organisms, harmless and excellent biocompatibility and a broad array of sources of the materials. PLA’s mechanical performance is closely related to its tacticity, because PLA with a high degree of tacticity and high degree of crystallinity have a wider range of applications. And thus the development of stereoselectivity catalysts is one of the priorities of the present study. However, the reports on efficient catalysts for the ROP of rac-LA to produce isotactic PLA are limited to Salen and Salan alumnium complexes.According to the above issues, in this dissertation, the research focuses on rare earth metals of great strategic significance which have been developed rapidly all the world in recent decades and are abundant in our country. We synthesised and characterised five [OOOO]-type tetradentate ligands. And obtained and characterised six unreported yttrium complexes by reacting these ligands with alkyl yttrium and amino yttrium. The molecular structure of complex1was established by single-crystal X-ray diffraction studies. The experiments show that these catalysts are active catalysts to polymerize rac-LA to give heterotactic PLA and isotactic PLA. Under room temperature, the Pr can be0.75,the Pm can reach up to0.87which is the highest among the isotactic PLA catalysed by rare earth metal catalysts under room temperature conditions.