Glass Transition Temperature Depression of Elastomers Blended with Poly(propene)s of Different Stereoregularities

Abstract

Glass temperature depression, measured by means of dynamic mechanical analysis, of elastomers blended together with isotactic, syndiotactic, and atactic poly(propene), PP, was detected for the first time. Two-phase melt blends consisting of PP and elastomers such as polystyrene-block-poly(ethene-co-1-butene)-block-polystyrene, SEBS, and poly(ethene-co-1-octene), EO, were prepared. The depression of the glass temperature, Tg, of PP/elastomer blends with respect to the Tg of the corresponding neat elastomer was attributed to thermally induced internal stress resulting from differential volume contraction of the two phases during cooling from the melt. The temperature dependence of the specific volume of the blend components was determined by pressure−volume−temperature measurements. The specific volume of the blend components was measured at temperatures varying between 30 and 270 °C and extrapolated to the elastomer Tg at −50 °C. This stress accumulation, reflected by glass temperature depression, is likely to influence mechanical properties, especially impact strength of PP/elastomer blends.