The surface composition profiles of bulk miscible and immiscible blends of atactic polypropylene ( a PP) with aspecific poly(ethylene- co -propylene) rubber ( a EPR) were studied by differential scanning calorimetry (DSC), sum frequency generation surface vibrational spectroscopy (SFG), and X-ray photoelectron spectroscopy (XPS). SFG spectra of blends of a PP and a EPR show that a PP preferentially segregates to the air/polymer interface, for both the bulk miscible and immiscible systems. The SFG spectra also indicate that methyl side branches assume a preferred configuration at the air/polymer interface, which may play a role in the high surface activity of a PP. Bulk miscibility is shown to control the thickness of the surface enrichment layer, with thicker enrichment layers detected by XPS on bulk immiscible blends. The thickness of the surface enrichment layer measured in the bulk miscible systems is in agreement with the thickness calculated using existing depth profiling models based on Flory−Huggins energy of mixing.
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Opdahl et al. (2002) studied this question.
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