Effects of Poly(Propylene Oxide)-Poly(Ethylene Oxide)-Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)-Poly(Propylene Oxide)-Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) ((EO)(n)-(PO)(m)-(EO)(n)) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO-PPO-PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO-PEO-PPO into PEO-PPO-PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO14-EO24-PO14 (17R4) was added to the Pluronics EO20-PO70-EO20 (P123), EO100-PO65-EO100 (F127), and EO133-PO50-EO133 (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol-gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.