Ring-Opening Alternating Copolymerization Of Cyclic Anhydrides/Epoxides Catalyzed By (Salen)Ti(?)Cl₂

Aliphatic polyesters,which combine both biodegradability and biocompatibility,have attracted much attention.The ring-opening alternating copolymerization(ROAC)of anhydride with epoxide provides a low energy,green and environmentally friend route for the preparation of biodegradable aliphatic polyesters.To develop high active and selective catalyst systems is a key topic in this field.Based on this consieration,the main contents of this paper were summarized as follows:1.Tetravalent titanium complexes with salen-type ligands were synthesized,characterized and tested as catalyst for the ring-opening alternating copolymerization(ROAC)of cyclic anhydrides and epoxides.These(salen)Ti(?)Cl₂complexes are structurally different from the typical(salen)M(?)Cl complexes(M=Al,Co and Cr),in which two Cl groups and no vacant coordination site exist in the axial positions.In the presence of bis(triphenylphosphine)iminium chloride(PPNCl),these(salen)Ti(?)Cl₂complexes could effectively catalyze the ROAC of phthalate anhydrides(PA)and cyclohexene oxide(CHO),affording perfectly alternating polyester.The Lewis acidity of complexes and structures of cocatalyst affected significantly on the catalytic activities.Meanwhile,(salen)Ti(?)Cl₂ system exhibited broad monomer adaptability,allowing for preparation of polyesters with structural diversity via copolymerization of some common cyclic anhydrides and epoxides.2.The stereoselective copolymerization of norbornene anhydride(NA)and epoxide by(salen)TiCl₂/PPNCl catalytic system were explored.We found that anhydride configuration,reaction temperature,and monomer feed ratio had significant effects on the epimerization side reaction.Polyester with different stereo-regularity could be easily prepared.