Synthesis, Characterization Of Bulky Zinc,sodium, And Potassium Metal Complexes And Application In The ROP Of Cyclic Esters

In recent decades, biodegradable polymer materials become a research hot spot,at present has been widely used in bio-pharmaceutical, food packaging, food,agriculture, and textile industry etc. Polylactide(PLA) as a typical representative,besides having the advantages of biodegradable and good biocompatibility, its raw materials come from the recycling of resources(corn and potatoes) and polymer can be degraded into non-toxic CO2 and H2 O. PLA was usually obtained by the ring opening polymerization of cyclic ester using metal complexes as initiator or catalyst.Although many excellent catalytic systems have been reported, but the catalytic system possessing non-toxic, high catalytic activity and high stereoselectivity is still rare. In this thesis, we designed and synthesized a series of big steric hindrance of zinc,sodium and potassium metal complexes and applied them in the ring-opening polymerization(ROP) of lactide. In addition, the mechanism of ROP and stereo-selectivity has also been studied.The thesis consists of the following parts:1. Introduction of the research progress of the catalytic ring-opening polymerization of lactide.2. Design and synthesis of a series of zinc complexes(1a-1d) and application in the ROP of L-lactide. Experimental results show these zinc phenoxides are highly active and excellent catalysts for immortal ROP of L-lactide giving isotactic poly-L-lactide with desirable molecular weights and low molecular weight distributions. Experiments also revealed steric hindrance and electronic effects have significant effects on the ROP of lactide with these zinc phenoxide complexes as catalysts.3. A series of zinc complexes(2-7) supported by Schiff base ligands were synthesized. These zinc complexes can be used as catalysts for the polymerization of rac-lactide in solution as well as in molten lactide, giving modest hetero-selectivities.Complex 2 even can catalyze the ROP of 1000 equivalents of rac-lactide with desirable molecular weight(Mn = 112500).4. A series of sodium and potassium phenolates(9a-9c and 10-15) were obtained by treating the simple ligands with crown ethers and KN(SiMe3)2/NaN(SiMe3)2respectively in toluene. These complexes can highly actively and isoselectively catalyze the polymerization of rac-lactide in toluene, getting the best isoselectivity of Pm value up to 0.89. The molecular weights of the obtained PLA were close to the expected values and the PDIs of the polymers were narrow. Experimental results alsodemonstrate that steric hindrance and electronic effects have significant effects on the behaviors of these catalysts in the ROP of rac-lactide.