Synthesis and Characterization of Biodegradable Multiblock Copolymers of L-Lactide, e-Caprolactone and Poly(ethylene glycol)

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