MICELLIZATION OF TRIBLOCK COPOLY(ETHYLENEOXIDE TETRAHYDROFURAN ETHYLENE-OXIDE)

The association behaviour of triblock copoly(ethylene oxide/tetrahydro furan/ethylene oxide), in particular E100T27E100, in aqueous solutions has been investigated by means of static and dynamic light scattering , nuclear magnetic resonance (NMR) and surface tension techniques. On raising the polymer concentration at room temperature, the copolymer a ggregates to form micelles with an aggregation number of about 105 (R- G,R- mic approximate to 15 nm and R-H,R- mic approximate to 13 nm, as revealed by light scattering and FT-PGSE NMR measurements, respectivel y). The micelles are kinetically quite stable, the micellar lifetime i s shown to be more than 1 h. The residence time of a single unimer in a micelle is more than 140 ms. The apparent radius of gyration R-G,R- mic is fairly independent of concentration, but large effects are obse rved on varying the temperature. Raising the temperature initially res ults in an increase of the apparent miceIlar size, followed by a maxim um at an intermediate temperature (approximate to 45 degrees C). At hi gher temperatures a contraction of the micelles is observed. The shape of the micelles also appear to vary in this temperature interval. The interactions responsible for these phenomena are discussed in terms o f, e.g., the temperature-dependent solubility of the alkylene oxide se gments in water and polydispersity effects.