Synthesis and characterization of biodegradable multiblock copolymers of L-lactide, "-caprolactone and poly(ethylene glycol)

Two multiblock copolymers of polyethylene glycol (PEG), L-lactide (LLA) and "-caprolactone (CL) were synthesized and characterized. Triblock prepolymers were rst synthesized using PEG with molecular weight (Mn) of 15,000 Daltons, "-caprolactone or L-lactide in the presence of Sn(Oct)2 as catalyst. The triblock PCL-b-PEG-b-PCL prepolymer with two hydroxyl functional groups was subjected to further block copolymerization with L-lactide in the presence of Sn(Oct)2 as catalyst. Similarly, the triblock PLLA-b-PEGb- PLLA prepolymer was subjected to further block copolymerization with "-caprolactone in the presence of the same catalyst. The molecular structures of the copolymers were characterized by 1H NMR and 13C NMR analyses. The thermal behavior and thermal stability of these copolymers were evaluated by DSC and TGA thermograms, respectively. Finally, the eect of each discrete block on thermal behavior and stability was studied in the typical pentablock copolymers.