| Abstract
| - Twenty-six poly(oxyethylene)-poly(oxybutylene) diblock copolymers were prepared by anionicpolymerization. The phase behavior of these copolymers was studied near the order−disorder transitionover the composition range from 0.21 to 0.84 poly(oxyethylene) volume fraction. Small-angle X-rayscattering was used to characterize phase transition temperatures and ordered state symmetries. Fourdistinct microstructures were observed: body-centered cubic, hexagonally packed cylinders (hex), lamellae(lam), and a bicontinuous cubic phase with Ia3̄d symmetry, together with a less well-defined region ofthe phase diagram comprising either hexagonally perforated layers or biphasic hex and lam. The Flory−Huggins parameter as a function of temperature was estimated using both the mean-field approximationand a fluctuation correction to the mean-field theory. The experimental microphase behavior is comparedwith the exact mean-field phase diagram calculated using self-consistent-field theory.
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