Synthesis And Characterization Of Rare Earth Metal Complexes And Their Applications In Ring-opening Polymerization Of Lactides

In recent years,due to the consumption of petrochemical resources and environmental protection requirements,polylactic acid(PLA)as one of the most innovative biopolymers,has been widely used in food packaging,agricultural and pharmaceutical fields.The catalysts for ring-opening polymerization of lactide monomers are mainly divided into metal catalysts and organic catalysts.Metal catalysts are the most widely used catalysts for ring-opening polymerization of lactide.Metal catalysts have the advantages of strong designability,wide selection range,and high activity.They provide higher polymerization rates at lower loadings,while maintaining good control for the molecular weight and stereoselectivity.Among them,rare earth metals have high catalytic activity,low toxicity,strong Lewis acidity,and diverse coordination modes,which have attracted great interest recently.In this paper,a series of rare earth metal complexes have been synthesized from bisphenol compounds and bis-ketiminate ligands derived from pyrazolinones.The effects of different rare earth ions and different ligands on the catalytic properties for the ROP of LA have been discussed.The specific contents are summarized as follows:Chapter One:A brief introduction to the development process and basic properties of polylactic acid,and a brief overview of the metal catalysts used in the ring-opening polymerization of lactide monomers.Chapter Two:Bisphenol ligands(2,2'-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol))MMPEP-H₂(L-H₂),RE[N(SiMe₃)₂]₃(RE=Y,La,Nd,Sm,Gd)and K[N(SiMe₃)₂]were reacted in a tetrahydrofuran solution at a ratio of 2:1:1 to synthesize a series of heterobimetellic potassium-rare metal complexes[REK(L)₂(THF)_n](RE=Y(1),La(2),Nd(3),Sm(4),Gd(5)).And rare earth metal complex 2a was obtained by the reaction of bisphenol ligand(L-H₂)and La[N(SiMe₃)₂]₃ at a ratio of 3:2.The composition and structures of these complexes were characterized by NMR,elemental analysis,X-ray single crystal diffraction analysis,and these complexes were used to catalyze the ring-opening polymerization of lactide.Complexes 1-5 have good controllability for the ring-opening polymerization of L-lactide and rac-lactide,and the obtained polymers have the actual molecular weight close to the theoretical molecular weight and narrow molecular distribution.At the same time,the catalytic rate has certain relationship with the metal ion radius.In addition,by comparing homometallic metal complexes and heterobimetallic complexes,it was found that rare earth ions played a major role in the ring-opening polymerization of lactide catalyzed by potassium-rare earth heterobimetic complexes.Chapter Three:bis-ketiminate ligands(L^1,2-H₂)using pyrazolinone as pro-ligand have been designed and synthesized,and react with RE[N(SiMe₃)₂]₃(RE=Y,La,Nd,Sm)to produce a series of rare earth metal complexes 6-13.At 30?,in 10mL of dichloromethane and benzyl alcohol using as an initiator,complexes 6-13 can effectively catalyze LA ring-opening polymerization and the conversions of L-LA are up to over 90%in 10 minutes.Using the methyl group replaced benzeneyl group as the substituent,the catalytic rates(complexes 10-13)are slightly faster than those of complexes 6-9.At the same time,MALDI-TOF mass spectrometry of the obtained oligomer showed the existence of a series of peaks with a mass of 144n+108+18(n(C₆H₈O₄)+BnOH+NH₄⁺),indicating that the obtained polymers were linear PLAs with-OCH₂Ph at one end and-OH at the other end.