Synthesis And Characterization Of Rare-Earth Metal Complexes Stabilized By Amino-Bridged Bis(phenolate) Ligands And Their Catalytic Performance On The Copolymerization Of L-lactide With Lactones

Polylactide has become a popular material because of its good biocompatibility and biodegradability.However,the inherent shortcomings of polylactide itself limit its scope of application.For example,their stabilities are not good enough,and the drug permeability is poor.In order to further expand the application of polylactide,the copolymerization of lactide and other lactones to prepare corresponding random copolymers is an effective way to improve the performance of polylactide.In this paper,we explored the copolymerization of lactide and caprolactone or butyrolactone to obtain more excellent biodegradable materials.This article uses a variety of amine-bridged bisaryloxy ligands to stabilize rare earth metal complexes.The following are the proligands used in this paper:[CH2N(4-CH3-C4H4)CH2-(2-OH-3,5-tBu2-C6H2)]2(H2L1);[CH2N(4-Cl-C4H4)CH2-(2-OH-3,5-tBU2-C6H2)]2(H2L2);[CH2N(4-OCH3-C4H4)CH2-(2-OH-3,5-tBu2-C6H2)]2(H2L3);(CH3)2NCH2CH2N[CH2-(2-OH-3,5-tBu2-C6H2)]2(H2L4);NH[CH2CH2N=CH(2-OH-3,5-tBu2C6H2)]2(H2L5).The main contents of copolymerization studied in this paper are as follows:1.Synthesis of rare earth amines stabilized by ethylenediamine-bridged bisaryloxy and its application to copolymerization of L-lactide and racemic ?-butyrolactone.RE[N(SiMe3)2]3(?-Cl)Li(THF)3(RE=Nd,Y,Yb)and the ligand precursors H2L1,H2L2,H2L3 are reacted in toluene to obtain L1YN(SiMe3)2(1),L1YbN(SiMe3)2(2),L2NdN(SiMe3)2(3),L2YN(SiMe3)2(4),L2YbN(SiMe3)2(5),L2YN(SiMe3)2(6),L2YbN(SiMe3)2(7).First,these complexes were used in the homopolymerization of racemic ?-butyrolactone to obtain an isotactic polyhydroxybutyrate.With the decrease of the central metal radius,the isotacticity will increase.When there are electron-withdrawing substituents on the ligand,the activity of catalyst will decreases.At room temperature,the isotacticity of the polymer is 0.72,and when the temperature is reduced to-20?,isotacticity can get to 0.81.Then,the complexe 6 and 7 were further applied to the copolymerization of lactide and butyrolactone.Using a one-step method,the conversion of lactide was finished within the first half an hour at 70?,but the conversion of butyrolactone was only 75%after 5 h,and it can not convert continuely even extend the reaction time.Finally,gradient copolymer was obtained.2.Random copolymerization of L-lactide and racemic ?-butyrolactone.Gradient copolymer was obtained by using side-arm ethylenediamine bisaryloxyyttrium complex L4YOCH2CF3(THF)(8)as an initiator,and random copolymer was obtained by using side-arm ethylenediamine bisaryloxy yttrium complex L4YbOCH2CF3(THF)(9).Also,even at ambient temperature,random copolymer can be obtained initiated by complex 9.Random copolymer were subjected to two-dimensional spectrum HMBC and HSQC nuclear magnetic characterization,then 1H NMR spectra were assigned in detail,and the average chain length of the copolymer was calculated.By adjusting the feed ratio of the two monomers,random copolymers with different composition were obtained at ambiant temperature.3.Copolymerization of L-lactide and ?-caprolactone.With rare earth metal complexes L5LaOC6H2-2,6-tBu2-4-CH3(THF)(10),L5LaOtBu(THF)(11),[L5LaOiPr]2(12),[L5LaOCH2Ph]2(13),[L5LaOEt]2(14)and[L5YOEt]2(15)act as catalysts to initiate the copolymerization of lactide and caprolactone.Random copolymers with segment lengthes of LLA=0.84,LCL=1.15 can be obtained through transesterification at room temperature.Also,the effects of different initiator groups,the radius of the metal and the temperature on the microstructure of the copolymer were explored.It was found that these initiator groups had little effect on the activity and selectivity of the copolymerization.However,if the central metal is yttrium with a small radius,the conversion of caprolactone and the randomness of the copolymer are both decrease,and the average link length of the two monomers increases slightly(LLA=1.77,LCL=1.49);temperature above 30? have little effect on the copolymer structure,and below the room temperature will inhibit the transesterification rate.Research on the mechanism of copolymerization shows that random copolymers are mainly formed by transesterification.