Effects of precipitate agents on temperature-responsive sol-gel transitions of PLGA-PEG-PLGA copolymers in water

This paper reports the effects of precipitate agents used in the collection of block copolymers composed of poly(lactic acid-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) on their thermogelling aqueous behaviors. We synthesized PLGA-PEG-PLGA triblock copolymers with a relatively wide distribution of molecular weight (MW) and then separated the crude polymers via three different precipitate agents (diethyl ether, hexane, or methanol). The obtained products exhibited, however, significantly different macroscopic states in water: some were sols, some were precipitates, and some underwent sol-gel transition upon heating. We found that by using different precipitate agents, ingredients of different MW were collected from the synthesized polymers, which accounted for the different states of the separated products in water. Our study strengthens the importance of an appropriate precipitate agent and reveals the subtle balance of hydrophobicity and hydrophilicity in this sort of amphiphilic block copolymers.