MICELLIZATION IN AQUEOUS-SOLUTION OF A POLY(ETHYLENE OXIDE) POLY(PROPYLENE OXIDE) POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMER INVESTIGATED WITH PULSED FIELD GRADIENT NMR

The self-diffusion behavior of a poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymer in aqueous solution was investigated with pulsed field gradient NMR. At temperatures <20-degrees-C the diffusion of the unimer was observed. In the temperature region between 20 and 40-degrees-C the transition to micelles occurs. The hydrodynamic radii of the unimer and the micelles were determined to 1.5 and 4.5 nm, respectively. They are independent of temperature and concentration in the concentration region between 1 and 10%. At about 70-degrees-C macroscopic phase separation and gelation occurs. The lifetime of a copolymer molecule within the micelle is shorter than the minimum observation time of our experiments (3 ms); therefore, we have always observed one (averaged) self-diffusion coefficient. Additional viscosity measurements support the results of the NMR investigations.