Calorimetric, X-ray scattering, and optical microscopy measurements have been used to characterize the morphology of two PEO-b-PS-b-PEO 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.

The complex dielectric permittivity has been measured for three poly(ethylenglycol)-bpoly(propylenglycol)-b-poly(ethylenglycol) copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10% and 20%, respectively). Only the noncrystalline sample shows the normal mode relaxation together with the segmental (α-relaxation) and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described by a VFT equation with the same value of T 0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the β-relaxation has been found. Near T g the β-relaxation time is close to the primitive time of the coupling model.

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