Calorimetric, X-ray scattering, and optical microscopy measurements have been used to characterize the morphology of two PEO-b-PS-b-I'EO copolymers. When the molecular weight of the PS block is much larger than the PEO one, the copolymer does not crystallize from the melt, and two well-separated glass transitions are clearly observed. The glass transition temperatures are different from those of the homopolymers; thus, phase segregation is not complete. For the case of blocks of similar molecular weight, the spherulites fill the whole sample, even if the degree of crystallinity is 60%; thus, the amorphous PS and PEO chains are sandwiched between the lamellae. The dynamics of the PEO chains has been studied by dielectric relaxation. In addition to the structural and the subvitreous relaxation modes, the crystalline copolymer shows a strong high-temperature relaxation that may be attributed to the Maxwell-Wagner interfacial process. It was found that the structure of the polymer does not affect the subvitreous process, but the structural relaxation is strongly dependent on whether the PEO chain is in an amorphous or crystalline sample. The temperature dependence of the relaxation times is compared with that reported in the literature for PS/PEO composites.