Synthesis And Characterization Of Aluminum, Zinc And Tin Complexes And Their Catalysis In The Ring-Opening Polymerization Of Cyclic Esters

Synthetic aliphatic polyesters such as PCL, PLA, PGA and PHB as well as their copolymers have attracted more and more interest due to their biocompatible, biodegradable and permeability properties which lead to applications drug delivery carrier, gene delivery carrier, resorbable sutures, degradable plastic, food packing, as well as scaffolds for tissue engineering. It is also proposed as a sustainable alternative to petrochemical-based polyolefins. The most effective way to synthesize the polymers is the ring-opening polymerization (ROP) of cyclic esters catalyzed or initiated by metal complexes. In the past several decades, lots of metal complexes as the catalysts/initiators have been designed and synthesized. Based on the previous works, we synthesized several series of metal complexes and studied their catalysis in the ROP ofε-CL and rac-LA. We also studied the structure-activity relationship of the catalysts. The work described in this thesis is summarized as the following:Chapter 1 introduces the development of biodegradable aliphatic polyesters and polymerization mechanism of lactones/lactides, especially the latest development of the metal catalysts, including Al, Sn, Zn and Mg complexes. The controlled stereoselective ROP of LA is well described.Chapter 2 is on the synthesis and characterization of aluminum and tin complexes supported by quinoline-based N,N,O-tridentate ligands and their catalysis in the controlled ROP ofε-CL. In the presence of benzyl alcohol (BnOH), all the aluminum complexes catalyze the ROP ofε-CL efficiently. In the absence of BnOH, the tin complexes catalyze the ROP ofε-CL, though they had lower catalytic activity. However, In the presence of BnOH, the tin complexes do not catalyze the ROP ofε-CL. The polymerization is controlled and gives polymer with controlled molecular weight and small polydispersity index (PDI).Chapter 3 presents the synthesis and characterization of dimethylaluminum iminophosphoranylenamides and their catalysis in the ROP ofε-CL. In the presence of BnOH, all the aluminum complexes catalyze the ROP ofε-CL efficiently. The polymerizations proceed in a living manner and give PCL with controlled molecular weight and small PDI. Compared to the aluminum complexes beringβ-diketiminate ligands, they show higher catalytic activity and better control to the polymerization.Chapter 4 describes the synthesis, characterization of the aluminum and zinc complexes bearing quinoline-based N,N,N-tridentate ligands and their catalysis towards the controlled ROP ofε-CL and rac-LA. In the presence of BnOH, all the aluminum and zinc complexes catalyze the ROP ofε-CL efficiently and the aluminum complexes show higher catalytic activity and better control in the polymerizations than the zinc complexes. In the presence of BnOH, the zinc complexes were efficient catalysts for the ROP of rac-LA, while the aluminum complexes have no catalytic activity under the same conditions. Kinetics studies revealed that the polymerizations proceed in a living manner.Chapter 5 is on the synthesis and characterization of bimetallic zinc and aluminum complexes and their catalysis in the controlled ROP ofε-CL and rac-LA. In the presence of BnOH, all the complexes catalyze the ROP ofε-CL and rac-LA efficiently. Kinetic studies reveal that the polymerization reactions catalyzed by the aluminum complexes follow first-order kinetics in the concentration of monomer and the molecular weight of the polymer is close to the theoretical value. In the presence of BnOH, all the bimetallic zinc complexes are efficient catalysts for the ROP ofε-CL . The zinc complex 5.12 also catalyzes the ROP of rac-LA, while 5.11 and 5.13 show no activity under the same conditions.Chapter 6 introduces the the synthesis and characterization of the aluminum complexes bearing enolic iminophosphinate O,N,N,O-tetradentate ligands and their catalysis towards the ROP ofε-CL and rac-LA. The structures of the aluminium complexes are very similar to the SALEN aluminum complexes reported in literature. Preliminary research results indicated that they are active catalysts in the ROP ofε-CL, but showed no catalytic activity in the ROP of rac-LA.