Thermoreversible micellization and gelation of a blend of pluronic polymers

Aqueous solutions of a blend consisting of a PEO-PPO-PEO triblock copolymer, Pluronic F127 (EO100-PO65-EO100) and a PPO-PEO-PPO triblock copolymer, Pluronic-R 25R4 (PO19-EO33-PO19) were studied. Thermoreversible micellization and gelation properties of the blend were examined as a function of temperature and molar ratio of 25R4 to F127 by means of micro DSC and rheology. The completely thermoreversible behaviors of micellization and gelation were observed for all the blend solutions with two F127 concentrations (10 and 15 wt%) and various 25R4/FI27 molar ratios (0-4) even though the pure 25R4 solution itself was not thermoreversible. At a given concentration of F127, three effects of 25R4 on F127 were found as follows. (a) The micellization temperature of F127 shifts to a lower temperature with increasing 25R4 content, implying a salt-out like effect of 25R4. (b) Beyond the primary peak for micellization a secondary peak appears due to the effect of 25R4. (c) At the molar ratio of 25R4/FI27 =3:1, the gelation of the 15 wt% F127 solution occurs twice at low and high temperatures, respectively. When the ratio > 3: 1, the gelation occurs only at high temperatures. The possible mechanisms involved in these unique behaviors of micellization and gelation have been proposed and discussed. The effect of 25R4 on F127 was compared with another Pluronic polymer F108 (EO133-PO50-EO133). (C) 2008 Elsevier Ltd. All rights reserved.