Ring-opening(co)polymerization Of Latones Catalyzed By Pyridyl-urea/base Systems

Aliphatic polyesters are a class of good biodegradable materials,including polylactide,polycaprolactone,polyvalerolactone,polyglycolide,etc.Due to their good biocompatibility,they have a good application prospect in drug-controlled release,tissue engineering and surgical suture,etc.In the preparation of such polyesters,various metal complex catalysts,such as Sn(Oct)2,were usually used in the polymerization.However,the toxicity of some residual metals limited their application in the medical field.Considering the safety,it is necessary to develop new non-toxic catalysts.Urea catalysts were a kind of organic countparts with good prospects in the ring-opening polymerization(ROP).Compared with metal catalysts,urea catalysts had a simple preparation and a mild operation.When used in combination with other cocatalysts,urea catalysts had a good activity in comparation with metal catalysts,which received increasing attention from researchers.This thesis mainly contained four parts,corresponding to four chapters as follows:In the first chapter,the research background of biodegradable polyester was introduced and the main catalytic systems in ROP were expounded.Based on the urea catalysts,the research progress of this kind of catalysts in recent years was summarized.And the research ideas and contents of this thesis were put forward.In the second chapter,more than ten pyridyl-urea catalysts with different substituent groups at different substitution positions were synthesized and further characterized by elemental analysis(EA),proton nuclear magnetic resonance(1H NMR),carbon nuclear magnetic resonance(13C NMR),and fourier transform infrared spectroscopy(FT-IR).The prepared catalysts were pure and in consistence with the design.In the third chapter,the activity of different urea catalysts was first compared in combination with 7-methyl-1,5,7-triazabicyclo[4.4.0]non-5-ene(MTBD)in the ROP of?-valerolactone(?-VL).It was found that 5X-/6X-PU(X=F,Cl,Br)had a better activity than others.The reaction conditions were further optimized with 6C-PU,and the effects of reaction temperature,type of organic base,and catalyst ratio on the reaction rate were investigated.The ROP of different equivalents of ?-VL were processed at 25 ? using 6C-PU in combination with MTBD.The prepared polymers had a narrow molecular weight distribution and the molecular weights were in agreement with theoretical values.The structure of synthesized polymers were characterized by 1H NMR,13C NMR,MALDITOF MS.Polyvalerolactones with cyclic sructure were prepared in the absence of benzyl alcohol.The 6C-PU/MTBD catalytic system was also used to catalyze the ROP of ?-caprolactone(?-CL)and trimethylene carbonate(TMC).Polymers with different molecular weights and different structure were prepared and characterized by 1H NMR and 13C NMR.The "Living Polymerization" behavior was confirmed by kinetic experiments and chain extension experiments,and the possible polymerization mechanism was predicted by NMR titration and dilution experiments.In the fourth chapter,the gradient copolymers of ?-VL and ?-CL were prepared by premixing the two momoners with 6C-PU/MTBD catalytic systems.Linear or cyclic copolymers were obtained in the presence or absence of benzyl alcohol,respectively.The composition of the copolymers could be adjusted by the variation of feeding ratios.Random and diblock copolymers were also prepared for comparison.The structure and thermal properties of the copolymers were characterized with kinetic experiment,NMR and DSC.