Synthesis, characterization, and stereocomplex-induced gelation of block copolymers prepared by ring-opening polymerization of L(D)-lactide in the presence of poly(ethylene glycol)

A series of block copolymers were synthesized by ring-opening polymerization of L(D)-lactide in the presence of mono- or dihydroxyl poly(ethylene glycol) (PEG) using zinc metal as a catalyst. The resulting diblock and triblock copolymers with relatively short polylactide (PLA) blocks were characterized by various analytical techniques such as H-1 NMR, SEC, DSC, and X-ray diffraction. The data showed that the copolymers were semicrystalline materials with predominant PEG crystallization although PLA blocks crystallized slightly in some cases. Solubilization tests showed that both the composition and molar mass are determining factors in the water solubility of the copolymers. Bioresorbable hydrogels were prepared from aqueous solutions containing both poly(L-lactide)/PEG and poly(D-lactide)/PEG block copolymers. Hydrogel formation resulted from stereocomplexation occurring between poly(L-lactide) and poly(D-lactide) blocks.