Abstract
Novel thermoreversible gelation behavior of aqueous solutions of ABAβtype triblock copolymers composed of the central polyethylene oxide (PEG) block and two poly(D,Lβlactic acidβcoβglycolic acid) side blocks was found. Phase transition characteristics, such as critical gel concentration (CGC) and lower and upper critical gel temperature (CGT), are closely related to the molecular structure of the triblock copolymers. The CGC and the lower CGT both increases with increasing PEG/PLGA molecular weight ratio. Increasing the GA content in PLGA block induces a somewhat higher CGC. The copolymer forms micelles with a PLGA loop core and a PEG shell in water. Also grouped micelles are identified seemingly due to the bridging of two micelles sharing two PLGA blocks of a block copolymer chain. As the temperature increases the association of micelles increases, which results in gelation. The ABAβtype copolymers exhibit a relatively low CGC (<10%) and low solβgel transition temperatures compared to BABβtype copolymers. As the temperature increases further gelβsol transition is observed, which would result from the shrinkage of micelles with temperature increase. The hydrodynamic size of the micelles is monitored by dynamic laser scattering, and a possible gelation mechanism was suggested. Β© 2002 Wiley Periodicals, Inc. J Biomed Mater Res 61: 188β196, 2002