The influence of the compression-molding temperature on the range of cocontinuity in polystyrene (PS)/ethylene-vinyl acetate (EVA) copolymer blends was studied. The blends presented a broad range of cocontinuity when compression-molded at 160°C, and they became narrower when compression-molded at higher temperatures. A coarsening effect was observed in PS/EVA (60:40 vol %) blends upon compression molding at higher temperature with an increase in the phase size of the cocontinuous structure. Concerning PS/EVA (40:60 vol %) blends, an increase in the mixing and molding temperatures resulted in a change from a cocontinuous morphology to a droplet-matrix morphology. This effect was observed by selective ex-traction experiments and scanning electron microscopy. The changes in the morphology with the molding conditions affected the storage modulus. An increase in the storage modulus in blends compression-molded at 160°C was observed as a result of dual-phase continuity. An EVA copolymer with a higher vinyl acetate content (28 wt %) and a higher melt-flow index resulted in blends with a broader range of cocontinuity. This effect was more pronounced in blends with lower amounts of PS, that is, when EVA formed the matrix.

A reactive compatibilizer, mercapto-functionalized EVA (EVASH), in combination with styrene-butadiene block copolymer (SBS), was used to compatibilize the blends of polystyrene (PS) and ethylene-vinyl acetate copolymer (EVA). The reactive compatibilization was confirmed by the presence of insoluble material and from dynamicmechanical analysis. In addition to a more uniform morphology with small phase size, the compatibilization also provided excellent stabilization of the morphology, with an almost complete suppression of coarsening during annealing. As a consequence, a substantial increase on the elongation at break without significant influence on ultimate tensile strength was achieved for compatibilized blends with different compositions.

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