Stereocomplex-Induced Gelation Properties of Polylactide/Poly(ethylene glycol) Diblock and Triblock Copolymers

The ring-opening polymerization of L- or D-lactide was realized in the presence of dihydroxyl or monomethoxy poly(ethylene glycol) (PEG) with a number-average molecular weight of 2000. The resulting low-molar-mass poly(L-lactide) (PLLA)/PEG and poly(D-lactide) (PDLA)/PEG triblock and diblock copolymers were characterized with nuclear magnetic resonance (NMR), differential scanning calorimetry, size-exclusion chromatography, and X-ray diffractometric analysis. Bioresorbable hydrogels were successfully prepared from aqueous solutions containing both copolymers because of interactions and stereocomplexation between the PLLA and PDLA blocks. Gelation was evaluated with the tube inverting method and rheological measurements. A phase diagram was realized with gel-sol transitions as a function of concentration. The rheological properties of the hydrogels were investigated under various conditions through changes in the copolymer concentration, temperature, time, and frequency. It was concluded that the hydrogels constituted a dynamic and evolutive system because of the continuous formation/destruction of cross-links and degradation. Further studies are underway to elucidate the degradation behavior and the potential of these substances as drug carriers or cell culture scaffolds. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1599-1606, 2011