Thermoreversible gel–sol behavior of biodegradable PCL‐PEG‐PCL triblock copolymer in aqueous solutions

A series of biodegradable PCL-PEG-PCL block copolymers were successfully synthesized by ring-opening polymerization of e-caprolactone initiated by poly(ethylene glycol) (PEG), which were characterized by 1H NMR, 13C NMR, and FTIR. Their aqueous solution displayed special gel–sol transition behavior with temperature increasing from 4 to 100°C, when the polymer concentration was above corresponding critical gel concentration (CGC). The gel–sol phase diagram was recorded using test tube inverting method and DSC method, which depended not only on chemical composition of copolymers, but also on heating history of copolymer's aqueous solution. As a result, the gel–sol transition temperature could be adjusted, which might be very useful for its application in biomedical fields such as injectable drug delivery system. And the typical shell-core structure of PCL-PEG-PCL micelles was introduced. The micelle-packing and partial crystallization might be the key gelation machanism for this gel–sol transition behavior of PCL-PEG-PCL aqueous solution. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 84B: 165–175, 2008