Thermal and swelling properties of polystyrene‐polyolefin blends

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Abstract
Model blends of glassy amorphous polystyrene and each of four different crystallizable and rubbery polyolefins of varying side‐chain molecular weight (polyethylene, polypropylene, poly(1‐butene), poly (4‐methyl‐1‐pentene)) have been prepared by melt extrusion of the polymeric components. Density measurements, differential scanning calorimetry (DSC), swelling measurements, and X‐ray diffraction have been performed on the extruded fibers. In all cases, over the entire range of blend composition, the polymeric blends are immiscible and incompatible. The DSC measurements indicated that the polystyrene Tg was not decreased after blending and that the small reductions in the crystallinity and melting point of the respective polyolefins was best explained by thermal and kinetic interference with homo‐crystallization of the respective polyolefins in the blends. The volumetric swelling and gravimetric sorption of n‐hexane in the various blends increased monotonically with polystyrene content. The companion experiments, relating axial swelling with polystyrene content, indicated that this particular mode of distension actually decreased with increasing polystyrene content. The composite results, including DSC, X‐ray, density, volumetric swelling and axial swelling suggest that the polystyrene phase is essentially microfibrillar and oriented in the direction of extrusion.