Glass transition temperature depression of elastomers blended with poly(propene)s of different stereoregularities

Glass temperature depression, measured by means of dynamic mechanical analy sis, of elastomers blended together with isotactic, syndiotactic, and atact ic poly(propene), PP, was detected for the first time. Two-phase melt blend s 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, T-g, of PP/elastomer ble nds with respect to the T-g of the corresponding neat elastomer was attribu ted to thermally induced internal stress resulting from differential volume contraction of the two phases during cooling from the melt. The temperatur e dependence of the specific volume of the blend components was determined by pressure-volume-temperature measurements. The specific volume of the ble nd components was determined by pressure-volume-temperature measurements. T he specific volume of the blend components was measured at temperatures var ying between 30 and 270 degrees C and extrapolated to the elastomer T-g at -50 degrees C. This stress accumulation, reflected by glass temperature dep ression, is likely to influence mechanical properties, especially impact st rength of PP/elastomer blends.