Domain Shape Transitions in Emulsified Polyolefin Blends

The shape of dispersed domains in emulsified polyolefin blends was studied by transmission electron microscopy. Model polyolefins polyethylene (PE), head-to-head polypropylene (PP), and PE−PP diblock copolymers were synthesized via anionic polymerization. Ternary blends with PE as the minor component were studied at 200 °C. All components are amorphous at this temperature. We find that increasing φ PE - PP /φ PE at constant φ PE - PP + φ PE leads to an abrupt transition from spherical domains to cell-like domains with faceted walls (where φ i is the volume fraction of component i). However, the cell-like domains were aggregated and formed large macrophases. The characteristic size of the domain-rich phase was considerably larger than the size of the PE droplets formed in the absence of the block copolymer. This indicates strong adhesive interactions between the cell-like domains. Current theories on emulsified polymer blends ignore interdomain interactions.