Synthesis Of Biodegradable Polyesters Promoted By Iron Compounds

With the development of technology and much attentions paid on environmental problems,the biodegradable polymer become the hot topic.As the representative biodegradable polymer,PCL and PLA attract many attentions.They are usually prepared by ring opening polymerization catalyzed by metal compounds.Sn(Oct)2 is most widely used in industry but the residence of Sn in polymer that are very harmful to human body,limited their application in biomaterial.Iron is the abundant element on the earth and also the essential element for human body,therefore,exploring the iron compounds as the catalyst for biodegradable polymer is very important.In this work,by using FeCl3 as the catalyst and tetradecanol as initiator,the ring opening polymerization of ε-caproclactone and copolymerization with L-lactide were investigated in detail.In addition,the effect of free ligand was also explored for ROP of ε-CL.The results showed FeCl3 can efficiently initiate the ring opening polymerization and polymerization conditions(such as molar ratio of monomer to iron,temperatures andtime)greatly affected the polymerization or copolymerization behavior.The microstructure analysis of the copolymer showed that PCL-b-PLA could be obtained only by with the first feed of CL and the second feed with of LA.The microstructure analysis of polymer suggested that ROP proceed in the coordination-insertion mechanism.The feeding of 1 equivalent free ligand in FeCl3 catalytic system in situ also greatly influenced the polymerization activity and the molecular weight of the polymer,which could be explained by the coordination of free ligand to FeCl3.Secondly,a series of bidentate iron(Ⅱ)complex(Fel-Fe5)bearing 4-arylimino-1,2,3-trihydroacridines were prepared and characterized by IR and EI-MS.The crystal structure of Fe5 showed it possessed the tetrahedron geometry around iron.In the presence of tetradecanol,the catalytic system by Fel-Fe5/2LiCH2SiMe3 in situ exhibited high efficiency toward the ring opening polymerization of ε-CL at room temperature,which is the rare example of efficient iron(Ⅱ)complexes for ROP of cyclic ester.1H NMR and MALDI-TOF analysis of resultant polymer clearly showed they are linear ones capped with tetradecyloxy.It was proposed that polymerization proceeded in coordination-insertion mechanism,in which the iron(Ⅱ)alkoxide generated in situ acted as the active species.