A Novel Multi-metal {(Salen) Al} Complexes: Synthesis Characterization And Stereo-selective Ring-opening Polymerization Of Rac-Lactides

Aliphatic polyesters which is biodegradable have great variety of application inbiology, biochemistry and pharmaceutical applications, such as poly(lactide),poly(glycolide), and poly(ε-caprolactone). This kind of polyester can be prepared bycondensation polymerization of hydroxyacid, or prepared by ROP reaction of lactoneor lactide.Among these reactions,condensation polymerization is anequilibrium reaction, and removing water from the system can be very difficult, bythis means hardly can we get a polymer with high molecular weight; on the otherhand, the ROP reaction is controllable by controling the catalyst and reactioncondition., therefore aliphatic polyesters with high molecular weight can besynthesized by some simple procedure. ROP reaction is the most widely used tosynthesize aliphatic polyesters. Catalyst is the key factor that determines whether thelactone and lactide is controllable, in recent years, the catalyst of ROP reaction oflactone and lactide is the focus of polymer chemistry research. In this essay, weproposed a kind of system in which can we synthesize a catalyst that catalysealuminum-based ROP reaction.the aluminum-based catalysts were synthesized by thereaction of aluminum with Schiff-base ligands, and at the same time, we synthesizeda double-center catalyst with serious steric hindrance that include silicon, and atri-center catalyst with special steric pattern. We continuely characterrized the twocatalysts, mainly on the catalysis performance, and we investigated the influence ofthe central substitute groups on the catalysis performance. We finally got the answerthat the two catalysts doesn,t only accomplish the control of the molecular weight ofracemic lactide(rac-LA), and moreover, in the polymerization procedure, it has highlysteric selectivity.