The growing AB block copolymer intermediate (PCL-PLA-OAi ) was extendedwith ethylene oxide at room temperature to form a HO-terminated PEO end-capped prepolymer which reacted with Teyssie catalyst

and replaced its isopropoxy groups toform an active prepolymeraupported catalyst

PCL-PLA-OCH2CH2-OAl . Ithas been proved that this prepolymer-supported catalyst was able to initiate CL polymerization in toluene at 90℃. The ABA triblocg copolymens with different length of segments with biodegradable as well as tough menbrane-forming properties have been synthesized successfully. This new synthetic method would provide a potential pothway from polylactide to form block copolymers with lactones.