Sythesis, Characterization Of C₃-trisphenol Based Bimetallic Complexes And Application In Ring-opening Polymerization Of Cyclic Esters

Polyester such as poly?lactide??PLA? and poly??-caprolactone??PCL? have drawn considerable attention due to their biocompatible, biodegradable, and permeable properties. These polymers can be prepared from the raw materials of corn, sugar and other natural crops, and they can degrade as water and carbon dioxide in the natural environment with few pollution. It not only reduces the spread of "white pollution" to a great extent but also effectively relieves the energy crisis of the oil and other resource exhausting. The physcally modified polymer products are widely used in our daily life through scientific modification, especially in the medical field due to their good biocompatibility, non-toxicity and other feather. A promising technique to prepare these renewably derived materials is the ring-opening polymerization?ROP? of the related cyclic esters employing metal complexes to afford expected polyesters with the prominent features of controlled molecular weight and low polydispersity?PDI?. In this thesis, the trisphenol ligand was synthesized, then a series of bimetallic complexes were prepared and their catalytic activity in the ring opening polymerization of cyclic esters was investigated.This thesis consists of three chapters:1. The ring-opening polymerization about cyclic esters was reviewed..2. Three bimetallic solvent-separated ion complexes [Li?thf?₄][AlMe?L?]?1? and [Li?thf?₄]₂[M?L?]₂?2, M = Zn; 3, M = Mg? have been synthesized and characterized. Treatment of a C₃-symmetric trisphenol ligand tris?3,5-di-tert-butyl-2-hydroxyphenyl?methane?H₃-L? with nBuLi and further reaction with Al?Me?₃, Zn?Et?₂, and Mg?nBu?₂ in THF provide 1–3 in quantitative yields, respectively. Complexes 2 and 3 could efficiently catalyze the ring-opening polymerization of L-lactide under a controlled manner, giving polymers with relatively narrow molecular weight distribution and desirable molecular weights, whereas complex 3 was not active in the polymerization. Experimental results show that the metal centers?Al, Zn and Mg? in anion parts of 1–3 can significantly influence the activity of catalysts in the polymerization, which may due to their different Lewis acidity.3. The methoxyl-bridged aluminium–lithium bimetallic complex [?L?Al??₂-OMe?Li?THF?₃]₂?4? was synthesized and structurally characterized. Reaction of 2,6-bis?3,5-bis-t-butyl-2-hydroxybenzyl?-4-t-butyl phenol?H₃–L? with n-Bu Li and Al?CH₃?₃ in a molar ratio of 1:1:1 in THF provides methylaluminium–lithium phenoxide [?L?Al?CH₃?Li]. Oxidation of the phenoxide by O₂ in air gives target product 4 in quantitative yield. Catalysis by complex 4 for ring-opening of ?-caprolactone??-CL? was systematically studied. Experimental results indicate that 4 could catalyze ?-CL with high conversion and narrow polydispersity even in an air atmosphere.