Interaction of Domains in Ternary Polymer Melt Blends with Separate Dispersions of the Inner Phases

The morphology evolution in three immiscible ternary polymer systems characterized by separate dispersions of the dispersed phases (i.e., no encapsulation phenomena takes place) was characterized. The components used were three of the following: commercial atactic poly(methyl methacrylate) (PMMA) and polystyrene (PS), crystallizable poly(butylene terephthalate) (PBT) and isotactic polypropylene (PP) and glass microspheres (GMS). In System I PMMA/PS/PP (primary dispersed phase/matrix/secondary, or minor, dispersed phase), all of the components were liquid on blending at 190°C. In System II PP/PS/PBT and System III PP/PSyGMS, at 190°C, the minor PBT and GMS dispersed phases were nondeformable. It was shown that small portions (0.5–1.0 wt%) of the PP minor dispersed phase added to the binary PMMA/PS blend produced a dual action: (a) transition of the PMMA dispersed phase to a cocontinuous one and (b) simultaneous substantial (up to a 6-fold) growth of the degree of dispersion of the blend. Moreover, these effects were accompanied by about a three-fold reduction of the threshold PMMA concentration (C*) at which it formed its own co-continuous phase in the ternary blend compared to that in the PMMA/PS binary mixture. The observed phenomena took place regardless of whether the domains of the minor dispersed phase were liquid (System I) or solid (Systems II and III), and was strongly related to the domain sizes of this phase and blend composition. A mechanism underlying the outlined behavior is proposed.