Ring-opening (Co)Polymerization Of Latones Catalyzed By Quinolinyl-urea/Base Systems

Aliphatic polyesters are widely used due to their excellent biodegradability.Metalbased catalysts are a popular class of catalysts used in the preparation of such polyesters,but their use in biomedical,packaging and agricultural applications is somewhat limited due to the toxicity of their residual metals.Therefore,it is particularly important to develop efficient and non-toxic catalysts.Urea catalysts are promising,they are relatively simple to prepare,inexpensive and easy to store.When used in combination with other types of catalysts,the catalytic effect of urea catalysts can be comparable to that of metal-based catalysts.The paper is divided into four main sections,corresponding to four chapters:(1)The research background of biodegradable polyesters is discussed,as well as the preparation methods of aliphatic polyesters and the main catalytic systems for the ring-opening polymerization reaction of lactone monomers.An in-depth analysis of the recent research progress of the catalytic system of(thio)urea/alkali combination is made,which provides valuable references for the research of this paper.(2)Six quinoline-urea catalysts were prepared from different substituted aminoquinolines with isocyanates.Characterization and analysis of their structures using elemental analysis(EA),fourier transform infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectroscopy(1H NMR)and carbon nuclear magnetic resonance spectroscopy(13C NMR),allowed the verification of the structures of the quinoline-urea catalysts.(3)Six quinoline-urea catalysts were combined with 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene(MTBD),using benzyl alcohol(BnOH)as initiator,to compare their catalytic activity for the ring-opening polymerization of 8-valerolactone(8-VL)proprieties.The results showed that the highest catalytic activity was obtained with the quinolyl-urea catalyst 3-QU substituted at position 3.Therefore,the combined 3QU/MTBD catalytic system was used for subsequent experimental studies in this paper.By studying different types of organic bases,different concentrations of catalysts and different reaction temperatures,the reaction conditions for the bulk polymerization of 8-VL can be better optimized.By controlling the[M]/[I]ratio,chain polyesters of different molecular weights can be prepared.Cyclic polyesters can be prepared when no initiator BnOH is added.After several experiments,it was found that the amount of catalyst used for the solution polymerization of δ-VL was higher than that for the bulk polymerization.After kinetic and chain expansion experiments,it was found that the reaction was characterized as an "active polymerization".The 3-QU/MTBD system can also be used effectively for the ring-opening polymerization of ε-caprolactone(ε-CL)and L-lactide(L-LA).The structure of the resulting polyester can be characterized by 1H NMR,13C NMR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI TOF MS),and the reaction process can be controlled and the product molecular weight distribution is narrow.(4)The 3-QU/MTBD system was used to catalyze the ring-opening copolymerization of ε-CL and L-LA,and the sequence structures of the copolyesters were analyzed using 1H NMR.The results show that the polymers prepared in the presence of premixed raw materials have a randomness R of approximately 0.5,which is intermediate between the fully random copolymers and the block copolymers.DSC data showed that PLA-co-PCL had poor crystallinity and no melt peaks were observed when the two monomers were in close proximity.PLA-b-PCL was prepared by the"one-pot" and "chain-expanding" methods,with controlled molecular sequences and Rvalues close to zero.