Temperature-Sensitive Sol-Gel Transition Behavior of Biodegradable Four-Arm Star-Shaped PEG-PLGA Block Copolymer Aqueous Solution

Abstract

Biodegradable four-arm star-shaped poly(ethylene glycol-b-DL-lactic acid-co-glycolic acid) block copolymers (4arm PEG-PLGA) were synthesized by ring-opening polymerization of DL-lactide and glycolide using 4arm PEG as an initiator and Sn(oct)(2) as a catalyst. In aqueous solution, they showed reversible sol to gel to sol transition behavior while increasing the temperature from 0 degrees C to 40 degrees C. The larger the molecular weight or the stronger the relative hydrophobicity of the hydrophobic PLGA block, the smaller the critical gel concentration (CGC). 4arm PEG-PLGA formed gels at lower CGC (13 wt %) than the inverse 4arm PLGA-PEG (24 wt %) due to the differences in their molecular structures.