Biodegradable thermosensitive micelles of PEG-PLGA-PEG triblock copolymers

Micellization of poly(ethylene glycol-b-(DL-lactic acid-co-glycolic acid)-b-ethylene glycol), PEG-PLGA-PEG, triblock copolymers in water was studied by C-13-NMR (nuclear magnetic resonance), dye solubilization method, and light scattering. Critical micelle concentration was decreased by half by increasing temperature from 20 to 50 degrees C. Enthalpy of micellization was calculated to be 10-20 KJ/mole. Apparent aggregation number, diameter of a micelle abruptly increased while second viral coefficient decreased at approximate to 30 degrees C suggesting that micellar growth as well as an increase in polymer-polymer attraction occur at this temperature. These findings might suggest that the sol to gel transition at high concentration of aqueous solutions of this polymer is driven by conformational changes of micelles. (C) 1999 Elsevier Science B.V. All rights reserved.