By means of low angle X‐ray scattering and differential scanning calorimetry, we have drawn the phase diagrams of block copolymers from styrene and ethylene oxide in the presence of a preferential solvent for poly(ethylene oxide) (PEO). Such systems exhibit two liquid crystalline structures in terms of temperature and solvent concentration. A lamellar structure with crystallized PEO chains (LCC) exists at temperatures below about 40°C and for solvent concentrations ranging from 0 to a value characteristic of the copolymer studied. For higher solvent concentrations and temperatures up to about 170°C a structure with method PEO chains is found. We have shown that in the LCC structure the chains of PEO crystallize in two layers; the solvent forms a third layer located between the PEO layers. This crystalline structure confirms the structure already proposed for the systems styrene‐ethylene oxide copolymer/diethyl phthalate. As the solvent concentration is increased, the thickness of the solvent layer increases, separating the PEO layers but without dissolving them; when the thickness of the PEO layers is high enough, the chains of PEO may crystallize on a lower thickness the number of folds being increased by one. We have studied the influence of the composition and relative molecular mass of the copolymer as well as the influence of the nature of the solvent on the variation of the structural parameters with solvent concentration.
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Gervais et al. (1973) studied this question.
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