| Abstract
| - The binary blends of poly(ethylene terephthalate) (PET) and poly(ether imide) (PEI) weremiscible in the melt but showed simultaneous crystallization and liquid−liquid demixing below the meltingpoint. In this study, the morphological structure induced by the coupling of crystallization and liquid−liquid phase separation in PET/PEI blends was probed by small-angle X-ray scattering (SAXS). For thesemicrystalline blends, a drastic intensity rise at low scattering angle superposed the scattering peakassociated with the lamellar stacks. This low-angular scattering was attributed to the electron densitycontrast between the “lamellar stack domains” (LS domains) consisting of alternating crystalline/amorphous layers and the PEI-rich domains located outside the LS domains. The scattering profileswere deconvoluted by applying the Debye−Bueche model to calculate the scattering intensity associatedwith the contrast between LS domains and PEI-rich domains. The morphological parameters, such ascrystal thickness, amorphous layer thickness, and long period, were subsequently determined from theintensity profile obtained by subtracting the Debye−Bueche contribution from the overall scatteringpattern. The crystal thickness of PET was unperturbed upon blending with PEI. A larger amorphouslayer thickness was identified in the blends, showing that some PEI was incorporated inside theinterlamellar regions after crystallization. Despite the swelling of the amorphous layer, the amorphouslayer thickness was relatively independent of the overall blend composition. Determination of the volumefraction of lamellar stacks from SAXS linear crystallinity and bulk crystallinity revealed the occurrenceof significant extralamellar placement of PEI when the overall PEI composition exceeded 20 wt %. Thismorphological structure is interpreted in terms of the simultaneous occurrence of liquid−liquid demixingand crystallization.
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