Living Ring-Opeing Polymerization Of ε-Caprolactone And L-and Rac-Lactides

Biodegradable polymers polycaprolactone(PCL) and polylactide (PLA) have found a wide range of applications, such as sutures, bone fracture fixation devices, drug controlled release carriers, tissue engineering scaffolds and green plastics for wrapping materials, disposal containers and fibers. They can be synthesized by ring-opening polymerization (ROP) of the caprolactone and lactide. We have synthesized two kinds of enolic Schiff base aluminum complexes containing ligands that differed in their steric properties. Their catalytic properties in the solution polymerization ofε-caprolactone(CL), L-lactide(L-LA) and racemic lactide (rac-LA) were examined. Factors that influenced the polymerization such as the structure of the catalysts, reaction parameters and polymerization mechanism were also discussed.A series of aluminum complexes based on cyclicβ-ketiminato ligands were synthesized and characterized. With 2-propanal as initiator, these well-defined complexes proved to be highly active towards ring-opening polymerization of L-lactide(L-LA) andε-caprolactone(CL). The highest conversion of CL is up to 99% and the highest conversion of L-LA is up to 90% under optimized condition. All polymers display crystalline with high molecular weights, and living character of L-lactide(L-LA) andε-caprolactone(CL) polymerization were achieved. Research result indicate the catalyst activity, polymer yield, and polymer molecular weight can be concrolled by variation of reaction parameters such as the reaction time and [M]O/[I]ratio.A series of "salen" aluminum complexes based on cyclicβ-ketiminato ligands were synthesized and characterized. Activated by 2-propanal as initiator, these complexes were proved to be highly active towards ring-opening polymerization of L-lactide(L-LA) and rac-lactide(rac-LA) and display as stereoselective catalysts. Though the DSC and WAXD data, the polymers were crystalline with high Tg and Tm. Research result indicates that the structures of the binary amine bridge have impact on activity. Polymer molecular weight and molecular weight distribution can be controlled by variation of reaction parameters.