The micellization in dilute aqueous solution of Pluronic copolymers P123 (E21P67E21) and F127 (E98P67E98) and mixtures of the two was investigated using static and dynamic light scattering. Gelation of concentrated solutions of the two copolymers and their mixtures was studied using tube inversion and oscillatory rheometry. The two copolymers comicellized to give micelles with narrow size distributions. Clouding temperatures and critical micelle temperatures decreased as the proportion of P123 in the mixture was increased. Micelle association numbers of the mixed micelles lay between the values found for micelles of P123 and F127 alone, whereas micelle radii passed through maximum values in the range 0-50 wt % P123. As judged by the ratio of the thermodynamic to the hydrodynamic radius, the micelle interaction potential changes gradually from soft to hard as the proportion of P123 in the mixture is increased. Regions of cubic and hexagonal (birefringent) gel were defined for concentrated solutions. The high-temperature boundary of the 30 wt % cubic gel decreased monotonically from 90 to 43 degrees C as the proportion of P123 in the mixture was increased from 0 to 100 wt %, whereas the low-temperature boundary was essentially constant at 15 +/- 3 degrees C. Increasing the proportion of P123 in the mixture at 25 degrees C increased the concentration at which the cubic gel was first formed and decreased the concentration at which the hexagonal gel was first formed.

Nineteen oxybutylene/oxyethylene/oxybutylene triblock copolymers [Bn/2EmBn/2, E ) oxyethylene, OCH2CH2; B ) oxybutylene, OCH2CH(CH2CH3)] were prepared and characterized. Twelve of the copolymers microphase-separated in the melt. Investigation of this microphase-separation behavior using small-angle X-ray scattering (SAXS) yielded values of the domain spacing (d-spacings) in the ordered phases and of the temperature of the order-disorder transition (TODT). In several cases the ordered phase structure was deduced from a combination of 1D and 2D SAXS and rheology. Values of TODT for the triblock copolymers were ca. 100 °C lower than those for EmBn diblock copolymers of identical composition and chain length but 30 °C higher if compared with diblock copolymers of half the triblock length. Values of the d-spacings indicated that the triblock copolymers were 10% more stretched than corresponding diblock copolymers. Determination of the Flory-Huggins parameter (χ) for the diblock and triblock systems gave identical results. The experimental results are compared with the prediction of mean-field theory.