Distribution of SIS compatibilizer in melt-mixed polystyrene-polyethylene homopolymer blends

This paper presents the results of transmission electron microscopy (TEM) studies on the distribution of polystyrene/polyisoprene/polystyrene (SIS) triblock copolymer compatibilizer in polystyrene-polyethylene homopolymer blends. The principal independent variable studied is the major-phase rheological properties (PS_major/PE_minor and PE_major/PS_minor blends). The polyisoprene block was preferentially stained by OsO₄ and could be clearly identified in cryo-ultramicrotomed TEM sections. The microstructural data show that when the rheologically strong PS phase is the major constituent, the compatibilizer follows the classical model localizing itself at the PS/PE interface. In the PE_major/PS_minor blends, however, the SIS compatibilizer is not localized at the PE/PS interface. Instead microdispersions of PS in SIS form which in turn are dispersed in the PE matrix. While the various microstructures are affected by the mixing protocol and polymer rheology, quiescent annealing after mixing indicates that the compatibilizer distribution is in part driven by thermodynamic effects.