Heterodinuclear Catalyst For The Copolymerization Of Epoxide And Lactone

Aliphatic polyester as a class of high-performance and versatile polymer materials,is considered to be one of the attractive,potential,and sustainable alternative to petroleum-based polymers.However,it often suffers from the drawbacks,such as hydrophobic and brittle due to their single structure nature,which limits its application in biomedical and pharmaceutical industries.Thus,modifications of polyester efficiently is of great theoretical significance and practical application,of which one efficient way is incorporating the aliphatic polyether segment into the main chain of the polyester.In present synthesis methods of polyether-polyester copolymers,it was difficult to accurately control molecular weight,despersity（D）,and ether-ester alternation.The research content of this paper is to design and synthesize a highly active catalytic system of bimetallic sites for mediating the copolymerization of epoxide and lactone,to obtain polyether polyester copolymers with controllable molecular weight,narrowDand adjustable ether ester content.The results are as follows:（1）Design and synthesis of a heterodinuclear catalyst system based on Co（III）-Zn or Co（III）-Al complexes with a rigid bridging biphenyl linker,which is capable of mediating the copolymerization of PO and CL.By investigating the effects of different metal catalyst systems,reaction temperatures,and feed ratios on the copolymerization activity and copolymer structure,it was found that that the heterodinuclear Co（III）-Al complex in conjunction with[PPN]Cl exhibited a good activity for the transformation to afford the corresponding poly（caprolactone-co-propylene oxide）with a number-average molecular weight（M_n=10.4 kg/mol）and a narrowDof 1.21.（2）The copolymerization of propylene oxide and caprolactone catalyzed by Co（III）-Al complex was studied in detail.The tracking experiments reveal that both PO and CL convert intothe polyether-polyester copolymers,without polyether or polyester homopolymer in the polymerization process.Furthermore,the molecular weight increased linearly and the dispersity remained unchanged with conversion of CL,indicating that the copolymerization had the characteristics of living polymerization.The competition polymerization,offering the monomer reactivity ratios of r_CL=0.96,r_PO=1.04（r is the ratio of the two reactive activities of homopolymerization and copolymerization in the competitive polymerization of the monomer,when r>1 indicates that the tendency of homopolymerization of the monomer is greater than that of copolymerization,r<1 indicates that the tendency of copolymerization is greater than that of homopolymerization）,suggest that the tendency of homopolymerization of the monomer or copolymerization was nearly identical,the ether segment and ester segment in copolymer were distributed randomly.It was further confirmed by the calculation result of density functional theory.Through DSC and TGA tests on the polyether-polyester copolymers with different ether content,it was found that with the increase of ether content in copolymer,the melting point of the copolymer decreased,but its decomposition temperature increases gradually,.The above results show that the thermal performance of the polyether-polyester copolymer can be adjustable by changing the proportion of ether/ester content of copolymers.